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Document and Entity Information Document - shares	3 Months Ended
Document and Entity Information Document - shares	Mar. 31, 2018	Apr. 30, 2018
Document Information [Line Items]
Entity Registrant Name	LEXICON PHARMACEUTICALS, INC./DE
Entity Central Index Key	0001062822
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		105,831,868

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 20,421	$ 61,661
Short-term investments	241,851	249,127
Accounts receivable, net of allowances of $4	4,482	4,825
Inventory	2,112	1,948
Prepaid expenses and other current assets	4,284	4,434
Total current assets	273,150	321,995
Property and equipment, net of accumulated depreciation and amortization of $59,067 and $58,623, respectively	17,244	17,687
Goodwill	44,543	44,543
Other intangible assets, net of accumulated amortization of $1,912 and $1,471, respectively	51,444	51,885
Other assets	432	429
Total assets	386,813	436,539
Current liabilities:
Accounts payable	66,553	57,652
Accrued liabilities	12,863	12,282
Current portion of deferred revenue	7,437	40,099
Current portion of long-term debt, net of deferred issuance costs	13,517	14,094
Total current liabilities	100,370	124,127
Deferred revenue, net of current portion	22,077	22,428
Long-term debt, net of deferred issuance costs	231,879	231,576
Deferred tax liabilities	6,014	6,014
Other long-term liabilities	279	292
Total liabilities	360,619	384,437
Commitments and contingencies
Equity:
Preferred stock, $.01 par value; 5,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $.001 par value; 225,000 shares authorized; 106,048 and 105,711 shares issued, respectively	106	106
Additional paid-in capital	1,438,625	1,435,526
Accumulated deficit	(1,409,267)	(1,381,404)
Accumulated other comprehensive loss	(394)	(222)
Treasury stock, at cost, 236 and 122 shares, respectively	(2,876)	(1,904)
Total equity	26,194	52,102
Total liabilities and equity	$ 386,813	$ 436,539

Balance Sheet Parenthetical (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Allowances for accounts receivable	$ 4	$ 4
Accumulated depreciation and amortization, property and equipment	59,067	58,623
Accumulated intangible assets amortization	$ 1,912	$ 1,471
Preferred stock, par value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000	5,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.001	$ 0.001
Common stock, shares authorized	225,000	225,000
Treasury stock, shares	236	122
Common Stock
Common stock, shares issued	106,048	105,711

Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Net product revenue	$ 5,460	$ 721
Collaborative agreements	19,665	17,565
Royalties and other revenue	82	7
Total revenues	25,207	18,293
Operating expenses:
Cost of sales (including finite-lived intangible asset amortization)	533	225
Research and development, including stock-based compensation of $1,655 and $1,184, respectively	47,783	43,581
Increase in fair value of Symphony Icon, Inc. purchase liability	0	2,101
Selling, general and administrative, including stock-based compensation of $1,419 and $1,047, respectively	14,857	14,871
Total operating expenses	63,173	60,778
Loss from operations	(37,966)	(42,485)
Interest expense	(5,114)	(1,588)
Interest and other income, net	1,005	530
Net loss before taxes	(42,075)	(43,543)
Income tax benefit	0	(8,652)
Net loss	$ (42,075)	$ (34,891)
Net loss per common share, basic and diluted	$ (0.40)	$ (0.33)
Shares used in computing consolidated net loss per common share, basic and diluted	105,668	104,461
Unrealized loss on investments	$ (172)	$ (69)
Comprehensive loss	$ (42,247)	$ (34,960)

Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock-based compensation expense associated with research and development expense	$ 1,655	$ 1,184
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,419	$ 1,047

Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Gain (Loss)	Treasury Stock
Balance, shares at Dec. 31, 2016		104,582
Balance, value at Dec. 31, 2016	$ 157,401	$ 105	$ 1,411,222	$ (1,250,363)	$ (195)	$ (3,368)
Cumulative effect from accounting change	0		1,991	(1,991)	0	0
Issuance of common stock to designees of Symphony Icon Holdings LLC, shares		660
Issuance of common stock to designees of Symphony Icon Holdings LLC, value	10,499	$ 0	10,499	0	0	0
Stock-based compensation	2,231	$ 0	2,231	0	0	0
Issuance of common stock under Equity Incentive Plans, shares		96
Issuance of common stock under Equity Incentive Plans, value	1,111	$ 0	1,111	0	0	0
Stock Issued During Period, Value, Treasury Stock Reissued	0		(3,143)	0	0	(3,143)
Repurchase of common stock	(1,679)	0	0	0	0	(1,679)
Net loss	(34,891)	0	0	(34,891)	0	0
Unrealized loss on investments	(69)	$ 0	0	0	(69)	0
Balance, shares at Mar. 31, 2017		105,338
Balance, value at Mar. 31, 2017	134,603	$ 105	1,423,911	(1,287,245)	(264)	(1,904)
Balance, shares at Dec. 31, 2017		105,711
Balance, value at Dec. 31, 2017	52,102	$ 106	1,435,526	(1,381,404)	(222)	(1,904)
Cumulative effect from accounting change	14,212	0	0	14,212	0	0
Issuance of common stock to designees of Symphony Icon Holdings LLC, value	0
Stock-based compensation	3,074	$ 0	3,074	0	0	0
Issuance of common stock under Equity Incentive Plans, shares		337
Issuance of common stock under Equity Incentive Plans, value	25	$ 0	25	0	0	0
Repurchase of common stock	(972)	0	0	0	0	(972)
Net loss	(42,075)	0	0	(42,075)	0	0
Unrealized loss on investments	(172)	$ 0	0	0	(172)	0
Balance, shares at Mar. 31, 2018		106,048
Balance, value at Mar. 31, 2018	$ 26,194	$ 106	$ 1,438,625	$ (1,409,267)	$ (394)	$ (2,876)

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (42,075)	$ (34,891)
Adjustments to reconcile consolidated net loss to net cash used in operating activities:
Depreciation and amortization	925	634
Increase in fair value of Symphony Icon, Inc. purchase liability	0	2,101
Stock-based compensation	3,074	2,231
Amortization of Debt Issuance Costs and Discounts	307	110
Deferred tax benefit	0	(8,652)
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	343	(1,241)
Increase in inventory	(164)	(236)
(Increase) decrease in prepaid expenses and other current assets	150	(6,498)
(Increase) decrease in other assets	(3)	33
Increase (decrease) in accounts payable and other liabilities	9,469	(24,703)
Decrease in deferred revenue	(18,801)	(14,384)
Net cash used in operating activities	(46,775)	(85,496)
Cash flows from investing activities:
Purchases of property and equipment	(40)	(92)
Purchases of investments	(46,892)	(60,905)
Maturities of investments	53,995	103,452
Net cash provided by investing activities	7,063	42,455
Cash flows from financing activities:
Proceeds from issuance of common stock	25	1,111
Repurchase of common stock	(972)	(1,679)
Repayment of debt borrowings	(581)	(536)
Net cash used in financing activities	(1,528)	(1,104)
Net increase (decrease) in cash and cash equivalents	(41,240)	(44,145)
Cash and cash equivalents at beginning of period	61,661	46,600
Cash and cash equivalents at end of period	20,421	2,455
Supplemental disclosure of cash flow information:
Cash paid for interest	774	332
Supplemental disclosure of non-cash investing and financing activities:
Common stock issued in satisfaction of Symphony Icon payment obligation	0	10,499
Unrealized loss on investments	(172)	(69)
Accumulated Deficit
Cash flows from operating activities:
Net loss	$ (42,075)	(34,891)
Supplemental disclosure of non-cash investing and financing activities:
Common stock issued in satisfaction of Symphony Icon payment obligation		$ 0

Summary of Significant Accounting Policies (Notes)

3 Months Ended

Mar. 31, 2018

Summary of Significant Accounting Policies [Abstract]

Significant Accounting Policies [Text Block]

Summary of Significant Accounting Policies

Basis of Presentation: The accompanying unaudited consolidated financial statements of Lexicon Pharmaceuticals, Inc. (“Lexicon” or the “Company”) have been prepared in accordance with generally accepted accounting principles for interim financial information and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements.

In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation have been included. Operating results for the three-month period ended March 31, 2018 are not necessarily indicative of the results that may be expected for the year ended December 31, 2018.

The accompanying consolidated financial statements include the accounts of Lexicon and its wholly-owned subsidiaries. Intercompany transactions and balances are eliminated in consolidation.

For further information, refer to the financial statements and footnotes thereto included in Lexicon’s annual report on Form 10-K for the year ended December 31, 2017, as filed with the SEC.

Use of Estimates: The preparation of financial statements in conformity with U. S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the period. Actual results could differ from those estimates.

Cash, Cash Equivalents and Short-Term Investments: Lexicon considers all highly-liquid investments with original maturities of three months or less to be cash equivalents. As of March 31, 2018 and December 31, 2017, short-term investments consist of U.S. treasury bills and corporate debt securities. The Company’s short-term investments are classified as available-for-sale securities and are carried at fair value, based on quoted market prices of the securities. The Company views its available-for-sale securities as available for use in current operations regardless of the stated maturity date of the security. Unrealized gains and losses on such securities are reported as a separate component of stockholders’ equity. Net realized gains and losses, interest and dividends are included in interest income. The cost of securities sold is based on the specific identification method.

Accounts Receivable: Lexicon records trade accounts receivable in the normal course of business related to the sale of products or services. Write-offs are evaluated on a case by case basis.

Inventory: Inventory is comprised of the Company’s approved product, XERMELO. Inventories are determined at the lower of cost or market value with cost determined under the specific identification method and may consist of raw materials, work in process and finished goods. Inventory consisted of the following:



	As of March 31,		As of December 31,
	2018		2017
	(in thousands)
Raw materials	$	617	$	616
Work-in-process	131		149
Finished goods	1,364		1,183
Total inventory	$	2,112	$	1,948

Concentration of Credit Risk: Lexicon’s cash equivalents, investments and accounts receivable represent potential concentrations of credit risk. The Company attempts to minimize potential concentrations of risk in cash equivalents and investments by placing investments in high-quality financial instruments. The Company’s accounts receivable are unsecured and are concentrated in pharmaceutical and biotechnology companies located in Europe and the United States. The Company has not experienced any significant credit losses to date.

Segment Information and Significant Customers: Lexicon operates in one business segment, which primarily focuses on the discovery, development and commercialization of pharmaceutical products for the treatment of human disease. Substantially all of the Company’s revenues have been derived from drug discovery alliances, target validation collaborations for the development and, in some cases, analysis of the physiological effects of genes altered in knockout mice, technology licenses, subscriptions to its databases, product sales, government grants and contracts and compound library sales.

Property and Equipment: Property and equipment that is held and used is carried at cost and depreciated using the straight-line method over the estimated useful life of the assets which ranges from three to 40 years. Maintenance, repairs and minor replacements are charged to expense as incurred. Leasehold improvements are amortized over the shorter of the estimated useful life or the remaining lease term. Significant renewals and betterments are capitalized.

Other Intangible Assets: Other intangible assets, net consist of in-process research and development acquired in business combinations, which are reported at fair value, less accumulated amortization. Intangible assets with finite lives are amortized using the straight-line method over their estimated useful lives. During the three months ended March 31, 2017, intangible assets relating to XERMELO of $24.7 million were reclassified from indefinite-lived to finite-lived assets once the FDA approved XERMELO. The Company recorded $0.4 million and $0.1 million in amortization expense related to this asset, which is recorded as cost of sales in the accompanying consolidated statements of comprehensive loss for the three months ended March 31, 2018 and 2017, respectively.

During the three months ended March 31, 2017, the Company’s valuation allowance for its deferred tax assets decreased by $8.7 million due to the reclassification of intangible assets relating to XERMELO from indefinite-lived to finite-lived assets, which resulted in the related deferred tax liability now being considered a source of taxable income. The Company recorded a $8.7 million deferred tax benefit with a corresponding reduction in its deferred tax liability in the three months ended March 31, 2017 as a result of this reclassification.

Impairment of Long-Lived Assets: Long-lived assets and certain identifiable intangible assets to be held and used are reviewed for impairment when events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by comparison of the carrying amount of an asset to future net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount that the carrying amount of the assets exceeds the fair value of the assets. Assets to be disposed of are reported at the lower of the carrying amount or fair value less costs to sell. There was no impairment of long-lived assets in the three months ended March 31, 2018 and 2017.

Indefinite lived intangible assets are also tested annually for impairment and whenever indicators of impairment are present. When performing the impairment assessment, the Company first assesses qualitative factors to determine whether it is necessary to recalculate the fair value of its intangible assets. If management believes, as a result of the qualitative assessment, that it is more likely than not that the fair value of the intangible assets is less than its carrying amount, the Company calculates the asset’s fair value. If the carrying value of the asset exceeds its fair value, then the intangible asset is written down to its fair value.

Goodwill Impairment: Goodwill is not amortized, but is tested at least annually for impairment at the reporting unit level. The Company has determined that the reporting unit is the single operating segment disclosed in its current financial statements. Impairment is the condition that exists when the carrying amount of goodwill exceeds its implied fair value. The first step in the impairment process is to determine the fair value of the reporting unit and then compare it to the carrying value, including goodwill. If the fair value exceeds the carrying value, no further action is required and no impairment loss is recognized. Additional impairment assessments may be performed on an interim basis if the Company encounters events or changes in circumstances that would indicate that, more likely than not, the carrying value of goodwill has been impaired. There was no impairment of goodwill in the three months ended March 31, 2018 and 2017.

Revenue Recognition:

Product Revenues

Product revenues consist of commercial sales of XERMELO in the United States and sales of bulk tablets of XERMELO to Ipsen Pharma SAS (“Ipsen”). Product revenues are recognized when the customer obtains control of the Company’s product, which occurs upon delivery to the customer. The Company recognizes product revenue net of applicable reserves for variable consideration, including allowances for customer credits, estimated rebates, chargebacks, discounts, returns, distribution service fees, and government rebates, such as Medicare Part D coverage gap reimbursements in the U.S. These estimates are based on the most likely amount method for relevant factors such as current contractual and statutory requirements, industry data and forecasted customer buying and payment patterns. The Company’s net product revenues reflect the Company’s best estimates of the amounts of consideration to which it is entitled based on the terms of the respective underlying contracts. Product shipping and handling costs are considered a fulfillment activity when control transfers to the Company’s customers and such costs are included in cost of sales.

Collaborative Agreements

Revenues under collaborative agreements include both license revenue and contract research revenue. The Company performs the following five steps in determining the amount of revenue to recognize as it fulfills its performance obligations under each of its agreements: (i) identify the contract(s) with a customer; (ii) identify the performance obligation in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligation in the contract, and (v) recognize revenue when (or as) the Company satisfies the performance obligation. The Company applies this five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company develops assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract.

At contract inception, the Company evaluates whether development milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal will not occur, the associated development milestone value is included in the transaction price. Development milestones that are not within the control of the Company or the licensee, including those requiring regulatory approval, are not considered probable of being achieved until those approvals are received. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue when (or as) the performance obligation is satisfied. At the end of each reporting period, the Company re-evaluates the probability of achievement of the development milestones and any related constraint, and if necessary, adjusts its estimates of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenues in the period of adjustment.

In agreements in which a license to the Company’s intellectual property is determined distinct from other performance obligations identified in the agreement, the Company recognizes revenue when the license is transferred to the licensee and the licensee is able to use and benefit from the license.

For agreements that include sales-based royalties, including milestones based on a level of sales, the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied).

The Company may receive payments from its licensees based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these agreements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.

Cost of Sales: Cost of sales consists of third-party manufacturing costs, freight and indirect overhead costs associated with sales of XERMELO. The Company began capitalizing inventory during the three months ended March 31, 2017 once the FDA approved XERMELO as the related costs were expected to be recoverable through the commercialization of the product. Costs incurred prior to approval of XERMELO have been recorded as research and development expense in the consolidated statements of comprehensive loss. As a result, cost of sales for approximately the next two years will reflect a lower average per unit cost of materials. Product shipping and handling costs are included in cost of sales. Cost of sales also includes the amortization of the in-process research and development intangible asset for XERMELO using the straight-line method over the estimated useful life of 14 years.

Research and Development Expenses: Research and development expenses consist of costs incurred for company-sponsored as well as collaborative research and development activities. These costs include direct and research-related overhead expenses and are expensed as incurred. Technology license fees for technologies that are utilized in research and development and have no alternative future use are expensed when incurred. Substantial portions of the Company’s preclinical and clinical trials are performed by third-party laboratories, medical centers, contract research organizations and other vendors. For preclinical studies, the Company accrues expenses based upon estimated percentage of work completed and the contract milestones remaining. For clinical studies, expenses are accrued based upon the number of patients enrolled and the duration of the study. The Company monitors patient enrollment, the progress of clinical studies and related activities to the extent possible through internal reviews of data reported to the Company by the vendors and clinical site visits. The Company’s estimates depend on the timeliness and accuracy of the data provided by the vendors regarding the status of each program and total program spending. The Company periodically evaluates the estimates to determine if adjustments are necessary or appropriate based on information it receives.

Stock-Based Compensation: The Company recognizes compensation expense in its consolidated statements of comprehensive loss for share-based payments, including stock options and restricted stock units issued to employees, based on their fair values on the date of the grant, with the compensation expense recognized over the period in which an employee is required to provide service in exchange for the stock award. Stock-based compensation expense for awards without performance conditions is recognized on a straight-line basis. Stock-based compensation expense for awards with performance conditions is recognized over the period from the date the performance condition is determined to be probable of occurring through the time the applicable condition is met.

The fair value of stock options is estimated at the date of grant using the Black-Scholes method. The Black-Scholes option-pricing model requires the input of subjective assumptions. Because the Company’s employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models do not necessarily provide a reliable single measure of the fair value of its employee stock options. For purposes of determining the fair value of stock options, the Company segregates its options into two homogeneous groups, based on exercise and post-vesting employment termination behaviors, resulting in a change in the assumptions used for expected option lives and forfeitures. Expected volatility is based on the historical volatility in the Company’s stock price. The Company utilized the Black-Scholes valuation model for estimating the fair value of the stock compensation granted, with the following weighted-average assumptions for options granted in the three months ended March 31, 2018 and 2017:



	Expected Volatility		Risk-free Interest Rate		Expected Term	Dividend Rate
March 31, 2018:
Employees	60	%	2.5	%	4	—	%
Officers and non-employee directors	63	%	2.8	%	8	—	%
March 31, 2017:
Employees	62	%	1.7	%	4	—	%
Officers and non-employee directors	71	%	2.3	%	8	—	%

The following is a summary of option activity under Lexicon’s stock-based compensation plans for the three months ended March 31, 2018:



	Options		Weighted Average Exercise Price
	(in thousands)
Outstanding at December 31, 2017	4,961		$	11.17
Granted	1,321		9.69
Exercised	(3	)	7.35
Expired	(170	)	14.23
Forfeited	(75	)	12.38
Outstanding at March 31,2018	6,034		10.74
Exercisable at March 31, 2018	3,253		$	10.89

During the three months ended March 31, 2018, Lexicon also granted its employees annual restricted stock units. Restricted stock units vest in three to four annual installments. The following is a summary of restricted stock units activity under Lexicon’s stock-based compensation plans for the three months ended March 31, 2018:



	Shares		Weighted Average Grant Date Fair Value
	(in thousands)
Outstanding at December 31, 2017	946		$	10.50
Granted	872		9.79
Vested	(334	)	9.85
Forfeited	(51	)	10.98
Outstanding at March 31, 2018	1,433		$	10.20

Income Taxes: The Tax Cuts and Jobs Act (the “2017 Tax Act”) was enacted on December 22, 2017. The 2017 Tax Act significantly changes U.S. corporate income tax laws, including reducing the U.S. corporate income tax rate from 35 percent to 21 percent beginning in 2018. At March 31, 2018, Lexicon has not completed the accounting for the tax effects of the 2017 Tax Act; however, an estimate of the effects on the existing deferred tax balances has been made, as further discussed below.

Lexicon recognizes deferred tax liabilities and assets for the expected future tax consequences of events that have been recognized differently in the financial statements and tax returns. Under this method, deferred tax liabilities and assets are determined based on the difference between the financial statement carrying amounts and tax bases of liabilities and assets using enacted tax rates and laws in effect in the years in which the differences are expected to reverse. Accordingly, in 2017 Lexicon remeasured certain deferred tax assets and liabilities based on the newly enacted U.S. corporate income tax rate, which resulted in a decrease of $171.4 million. Lexicon will continue to make and refine calculations and estimates, which could potentially affect the measurement of the deferred tax balances or give rise to new deferred tax assets. Where the Company has not yet been able to make reasonable estimates of the impact of certain elements, the Company has not recorded any amounts related to those elements and has continued accounting for them in accordance with ASC 740 on the basis of the tax laws in effect immediately prior to the enactment of the 2017 Tax Act. Deferred tax assets are evaluated for realization based on a more-likely-than-not criteria in determining if a valuation allowance should be provided.

Net Loss per Common Share: Net loss per common share is computed using the weighted average number of shares of common stock outstanding. Shares associated with convertible debt, stock options and restricted stock units are not included because they are antidilutive.

Recent Accounting Pronouncements Level 1 (Notes)	3 Months Ended
Recent Accounting Pronouncements Level 1 (Notes)	Mar. 31, 2018
Recent Accounting Pronouncements [Abstract]
New Accounting Pronouncements, Policy	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, “Revenue from Contracts with Customers”, which amends FASB ASC Topic 606. ASU 2014-09 provides a single, comprehensive revenue recognition model for all contracts with customers. This standard contains principles for the determination of the measurement of revenue and the timing of when such revenue is recognized. Revenue recognition will reflect the transfer of goods or services to customers at an amount that is expected to be earned in exchange for those goods or services. In 2015, the FASB issued ASU No. 2015-14, “Revenue from Contracts with Customers: Deferral of Effective Date”, which deferred the effective date by one year to annual periods after December 15, 2017 including interim periods within that reporting period. In 2016, the FASB issued four additional ASUs related to Topic 606: ASU Nos. 2016-08, 2016-10, 2016-12 and 2016-20. These ASUs clarify various aspects of the new revenue guidance, including principal versus agent considerations, identifying performance obligations and licensing, and they include other improvements and practical expedients. The Company adopted this new standard on January 1, 2018 using the modified retrospective transition method, and has applied the provisions to contracts that were not complete as of January 1, 2018. Impact of Adoption The Company recognizes product revenue when the customer obtains control of the product, which occurs upon delivery. Product revenue is recorded net of applicable reserves for variable consideration, including discounts and allowances. These estimates are based on the most likely amount method for relevant factors such as current contractual and statutory requirements, industry data and forecasted customer buying and payment patterns. The Company’s net product revenues reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the respective underlying contracts. The adoption of this ASU did not impact the timing or amount of revenues recognized related to its contracts with customers for the sale of product. The Company’s primary source of collaboration revenue has been through its license and collaboration agreements with three separate third-party licensees: Texas Institute for Genomic Medicine (“TIGM”), Sanofi and Ipsen. With respect to its contract with TIGM, the Company evaluated the variable consideration relating to the remaining milestone and determined, based on the most likely amount method, that it was not probable that a significant reversal would occur and therefore, concluded no constraint was required. Accordingly, the Company recorded a $14.2 million cumulative-effect adjustment to its accumulated deficit as of January 1, 2018 and reduced deferred revenue in the same amount. With respect to its collaboration agreements with Sanofi and Ipsen, the Company evaluated the variable consideration relating to future milestone payments and determined, based on the most likely amount method, that the estimated amounts could be considered as part of the transaction price. The Company then evaluated the variable constraint and determined that the variable consideration amounts are constrained, primarily by future events that are not within the control of the Company. The future events primarily relate to receipt of positive results from studies, approval from regulatory agencies, and upon achieving sales in certain locations. Accordingly, the Company determined that there was no cumulative adjustment required for these agreements on the date of adoption. In February 2016, the FASB issued ASU No. 2016-02, “Leases.” ASU 2016-02 requires companies that lease assets to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its balance sheet. The pronouncement will also require additional disclosures about the amount, timing and uncertainty of cash flows arising from leases. This pronouncement is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, and early adoption is permitted. This ASU is required to be adopted using a modified retrospective approach. Management plans to adopt ASU 2016-02 on January 1, 2019, and anticipates that most of its operating leases will result in the recognition of additional assets and corresponding liabilities on the consolidated balance sheets. The Company does not expect that the implementation of the ASU will have a material impact on its financial position. The actual impact will depend on the Company’s lease portfolio at the time of adoption. The Company continues to assess all implications of the standard and related financial disclosures.

Fair Value Measurements

3 Months Ended

Mar. 31, 2018

Fair Value Measurements [Abstract]

Fair Value, Measurement Inputs, Disclosure

Fair Value Measurements

The Company uses various inputs in determining the fair value of its investments and measures these assets on a recurring basis. Assets and liabilities recorded at fair value in the consolidated balance sheets are categorized by the level of objectivity associated with the inputs used to measure their fair value. The following levels are directly related to the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities:


•	Level 1 - quoted prices in active markets for identical investments, which include U.S. treasury securities


•	Level 2 - other significant observable inputs (including quoted prices for similar investments, market corroborated inputs, etc.), which includes corporate debt securities


•	Level 3 - significant unobservable inputs

The inputs or methodology used for valuing securities are not necessarily an indication of the credit risk associated with investing in those securities. The following table provides the fair value measurements of applicable Company assets and liabilities that are measured at fair value on a recurring basis according to the fair value levels described above as of March 31, 2018 and December 31, 2017:



	Assets and Liabilities at Fair Value as of March 31, 2018
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets
Cash and cash equivalents	$	20,421	$	—	$	—	$	20,421
Short-term investments	213,985		27,866		—		241,851
Total cash and cash equivalents and investments	$	234,406	$	27,866	$	—	$	262,272



	Assets and Liabilities at Fair Value as of December 31, 2017
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets
Cash and cash equivalents	$	61,661	$	—	$	—	$	61,661
Short-term investments	222,148		26,979		—		249,127
Total cash and cash equivalents and investments	$	283,809	$	26,979	$	—	$	310,788

The Company did not have any Level 3 assets or liabilities as of March 31, 2018 or December 31, 2017. In March 2017, the Company satisfied its remaining contingent payment obligation to designees of Symphony Icon Holdings LLC. Prior to payment, the Symphony Icon purchase consideration liability, a Level 3 liability, was estimated using a probability-based income approach utilizing an appropriate discount rate. Changes in the fair value of the Symphony Icon purchase consideration liability were recorded as an increase or decrease in Symphony Icon purchase liability expense in the accompanying consolidated statements of comprehensive loss. The change in fair value of the purchase consideration liability was an increase of $2.1 million during the three months ended March 31, 2017.

The Company also has assets that under certain conditions are subject to measurement at fair value on a non-recurring basis. These assets include goodwill associated with the acquisitions of Coelacanth Corporation in 2001 and Symphony Icon in 2010 and intangible assets associated with the acquisition of Symphony Icon in 2010. See Note 6, Arrangements with Symphony Icon, Inc., for additional information. For these assets, measurement at fair value in periods subsequent to their initial recognition is applicable if one or more is determined to be impaired.

Cash and Cash Equivalents and Investments

3 Months Ended

Mar. 31, 2018

Cash and Cash Equivalents and Investments [Abstract]

Cash and Cash Equivalents Disclosure

Cash and Cash Equivalents and Investments

The fair value of cash and cash equivalents and investments held at March 31, 2018 and December 31, 2017 are as follows:



	As of March 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	20,421	$	—	$	—		$	20,421
Securities maturing within one year:
U.S. treasury securities	214,302		—		(317		)	213,985
Corporate debt securities	27,943		—		(77		)	27,866
Total short-term investments	$	242,245	$	—	$	(394	)	$	241,851
Total cash and cash equivalents and investments	$	262,666	$	—	$	(394	)	$	262,272

	As of December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	61,661	$	—	$	—		$	61,661
Securities maturing within one year:
U.S. treasury securities	222,316		—		(168		)	222,148
Corporate debt securities	27,033		—		(54		)	26,979
Total short-term investments	$	249,349	$	—	$	(222	)	$	249,127
Total cash and cash equivalents and investments	$	311,010	$	—	$	(222	)	$	310,788

There were no realized losses for the three months ended March 31, 2018, and $7,000 in realized losses for the three months ended March 31, 2017. The cost of securities sold is based on the specific identification method.

Debt Obligations	3 Months Ended
Debt Obligations	Mar. 31, 2018
Debt Obligations [Abstract]
Debt Disclosure	Debt Obligations Convertible Debt. In November 2014, Lexicon completed an offering of $87.5 million in aggregate principal amount of its 5.25% Convertible Senior Notes due 2021 (the “Convertible Notes”). The conversion feature did not meet the criteria for bifurcation as required by generally accepted accounting principles and the entire principal amount was recorded as long-term debt on the Company’s consolidated balance sheets. The Convertible Notes are governed by an indenture (the “Indenture”), dated as of November 26, 2014, between the Company and Wells Fargo Bank, N.A., as trustee. The Convertible Notes bear interest at a rate of 5.25% per year, payable semiannually in arrears on June 1 and December 1 of each year, beginning on June 1, 2015. The Convertible Notes mature on December 1, 2021. The Company may not redeem the Convertible Notes prior to the maturity date, and no sinking fund is provided for the Convertible Notes. Holders of the Convertible Notes may convert their Convertible Notes at their option at any time prior to the close of business on the business day immediately preceding the maturity date. Upon conversion, the Company will deliver for each $1,000 principal amount of converted Convertible Notes a number of shares of its common stock equal to the conversion rate, as described in the Indenture. The conversion rate is initially 118.4553 shares of common stock per $1,000 principal amount of Convertible Notes (equivalent to an initial conversion price of $8.442 per share of common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, the Company will increase the conversion rate for a holder who elects to convert its Convertible Notes in connection with such a corporate event in certain circumstances. If the Company undergoes a fundamental change, holders may require the Company to repurchase for cash all or any portion of their Convertible Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Convertible Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In connection with the issuance of the Convertible Notes, the Company incurred $3.4 million of debt issuance costs. The debt issuance costs are amortized as interest expense over the expected life of the Convertible Notes using the effective interest method. The Company determined the expected life of the debt was equal to the seven-year term of the Convertible Notes. As of March 31, 2018, the balance of unamortized debt issuance costs was $1.8 million, which offsets long-term debt on the consolidated balance sheets. The fair value of the Convertible Notes was $111.9 million as of March 31, 2018 and was determined using Level 2 inputs based on the indicative pricing published by certain investment banks or trading levels of the Convertible Notes, which are not listed on any securities exchange or quoted on an inter-dealer automated quotation system. Mortgage Loan. In April 2004, Lexicon obtained a $34.0 million mortgage on its facilities in The Woodlands, Texas. The mortgage loan originally had a ten-year term with a 20-year amortization and a fixed interest rate of 8.23%. The mortgage has been amended to extend the maturity date to October 2018, with the mortgage loan’s monthly payment amount and fixed interest rate each remaining unchanged. The mortgage had a principal balance outstanding of $13.5 million as of March 31, 2018. This entire balance is recorded as current portion of long-term debt in the accompanying consolidated balance sheet as of March 31, 2018 as there is a balloon payment due in October 2018. The buildings and land that serve as collateral for the mortgage loan are included in property and equipment at $59.2 million and $2.7 million, respectively, before accumulated depreciation, as of March 31, 2018. The fair value of Lexicon’s mortgage loan approximates its carrying value. The fair value of Lexicon’s mortgage loan was determined using Level 2 inputs using discounted cash flow analysis, based on the Company’s estimated current incremental borrowing rate. BioPharma Term Loan. In December 2017, Lexicon entered into a loan agreement with BioPharma Credit PLC and BioPharma Credit Investments IV Sub LP that provides up to $200.0 million borrowing capacity (the “BioPharma Term Loan”) available in two tranches, each maturing in December 2022. The BioPharma Term Loan bears interest at 9% per year, subject to additional interest if an event of default occurs and is continuing, and is payable quarterly. A tranche of $150.0 million was funded in December 2017. The BioPharma Term Loan is subject to mandatory prepayment provisions that require prepayment upon a change of control or receipt of proceeds from certain non-ordinary course transfers of assets. The Company may prepay the BioPharma Term Loan in whole at its option at any time. Any prepayment of the BioPharma Term Loan is subject to customary make-whole premiums and prepayment premiums. The Company’s obligations under the BioPharma Term Loan are secured by a first lien security interest in substantially all of the assets of the Company and certain of its subsidiaries. The loan agreement contains certain customary representations and warranties, affirmative and negative covenants and events of default applicable to the Company and certain of its subsidiaries, including among other things, covenants restricting dispositions, fundamental changes in the business, mergers or acquisitions, indebtedness, encumbrances, distributions, investments, transactions with affiliates and subordinated debt. If an event of default occurs and is continuing, all amounts outstanding under the BioPharma Term Loan may be declared immediately due and payable. In connection with the BioPharma Term Loan, the Company incurred $4.1 million of debt issuance costs. The debt issuance costs are amortized as interest expense over the expected life of the BioPharma Term Loan using the effective interest method. The Company determined the expected life of the debt was equal to the five-year term of the BioPharma Term Loan. As of March 31, 2018, the balance of unamortized debt issuance costs was $3.9 million, which offsets long-term debt on the consolidated balance sheets. The fair value of the BioPharma Term Loan approximates its carrying value. The fair value of the BioPharma Term Loan was determined using Level 2 inputs using discounted cash flow analysis, based on the Company’s estimated current incremental borrowing rate.

Arrangements with Symphony Icon Inc	3 Months Ended
Arrangements with Symphony Icon Inc	Mar. 31, 2018
Arrangements with Symphony Icon Inc [Abstract]
Arrangements with Symphony Icon Inc	Arrangements with Symphony Icon, Inc. On June 15, 2007, Lexicon entered into a series of related agreements providing for the financing of the clinical development of certain of its drug candidates, including XERMELO, along with any other pharmaceutical compositions modulating the same targets as those drug candidates (the “Programs”). The agreements included a Novated and Restated Technology License Agreement pursuant to which the Company licensed to Symphony Icon, a then wholly-owned subsidiary of Symphony Icon Holdings LLC (“Holdings”), the Company's intellectual property rights related to the Programs. Holdings contributed $45 million to Symphony Icon in order to fund the clinical development of the Programs. Under a Share Purchase Agreement, dated June 15, 2007, between the Company and Holdings, the Company issued and sold to Holdings 1,092,946 shares of its common stock on June 15, 2007 in exchange for $15 million and an exclusive purchase option (the “Purchase Option”) that gave the Company the right to acquire all of the equity of Symphony Icon, thereby allowing the Company to reacquire all of the Programs. On July 30, 2010, Lexicon entered into an Amended and Restated Purchase Option Agreement (the “Purchase Option Agreement”) with Symphony Icon and Holdings and simultaneously exercised the Purchase Option, thereby reacquiring the Programs. Pursuant to the amended terms of the Purchase Option, Lexicon paid Holdings $10 million on July 30, 2010 and issued 1,891,074 shares of common stock to designees of Holdings on July 30, 2012 in satisfaction of an additional $35 million base payment obligation. Lexicon also agreed to make up to $45 million in additional contingent payments, which would consist of 50% of any consideration Lexicon receives pursuant to any licensing transaction (a “Licensing Transaction”) under which Lexicon grants a third party rights to commercialize XERMELO or other pharmaceutical compositions modulating the same target as XERMELO (the “LG103 Programs”), subject to certain exceptions. The contingent payments would be due if and when Lexicon receives such consideration from a Licensing Transaction. In the event Lexicon received regulatory approval in the United States for the marketing and sale of any product resulting from the LG103 Programs prior to entering into a Licensing Transaction for the commercialization of such product in the United States, in lieu of any contingent payment from such a Licensing Transaction, Lexicon would pay Holdings the sum of $15 million and the amount of certain expenses Lexicon incurred after its exercise of the Purchase Option which were attributable to the development of such product, reduced by up to 50% of such sum on account of any contingent payments paid prior to such United States regulatory approval attributable to any such Licensing Transaction outside of the United States with respect to such product. In the event Lexicon made any such payment upon United States regulatory approval, Lexicon would have no obligation to make subsequent contingent payments attributable to any such Licensing Transactions for the commercialization of such product outside the United States until the proceeds of such Licensing Transactions exceed 50% of the payment made as a result of such United States regulatory approval. The contingent payments were payable in cash or a combination of cash and common stock, in Lexicon’s discretion, provided that no more than 50% of any contingent payment would be paid in common stock. In December 2014, Lexicon paid $5.8 million in cash and issued 666,111 shares of common stock to designees of Holdings in satisfaction of a $11.5 million contingent payment obligation as a result of receiving an upfront payment pursuant to Lexicon’s license and collaboration agreement with Ipsen. In April 2015, Lexicon paid $0.75 million in cash to Holdings in satisfaction of its contingent payment obligation as a result of receiving an additional upfront payment from Ipsen in March 2015. In September 2016, Lexicon paid $3.2 million in cash to Holdings in satisfaction of its contingent payment obligation as a result of receiving a milestone payment from Ipsen in August 2016 (see Note 8, Collaboration and License Agreements). In September 2016, Lexicon entered into an amendment (the “Amendment”) to the Purchase Option Agreement with Holdings and Symphony Icon pursuant to which Lexicon agreed to pay Holdings $21.0 million upon Lexicon’s receipt of regulatory approval in the United States for the marketing and sale of XERMELO, such buyout amount to be in lieu of any remaining payments which may be or become payable to Holdings under the Purchase Option Agreement. In March 2017, Lexicon paid $10.5 million in cash and issued 659,905 shares of common stock to designees of Holdings in satisfaction of its remaining contingent payment obligation as a result of receiving regulatory approval in the United States for the marketing and sale of XERMELO. Lexicon accounted for the exercise of the Purchase Option and acquisition of Symphony Icon as a business combination. In connection with its acquisition of Symphony Icon, Lexicon paid $10.0 million in cash, and also agreed to pay Holdings additional base and contingent payments as discussed above. The fair value of the base and contingent consideration payments was $45.6 million and was estimated by applying a probability-based income approach utilizing an appropriate discount rate. This estimation was based on significant inputs that are not observable in the market, referred to as Level 3 inputs. Key assumptions include: (1) a discount rate of 14% for the base payments; (2) a discount rate of 18% for the contingent payments; and (3) a probability adjusted contingency. No discount rate was used in the valuation of the contingent consideration liability as of December 31, 2016 as the expected buyout was short-term in nature. As programs progressed, the probability adjusted contingency was adjusted as necessary. Subsequent changes in the fair value of the Symphony Icon purchase consideration liability were recorded as increase or decrease in fair value of Symphony Icon purchase liability expense in the accompanying consolidated statements of comprehensive loss. The fair value of the Symphony Icon purchase consideration liability increased by $2.1 million during the three months ended March 31, 2017.

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2018
Commitments and Contingencies [Abstract]
Commitments and Contingencies Disclosure	Commitments and Contingencies Operating Lease Obligations: A Lexicon subsidiary leases office space in Basking Ridge, New Jersey under an operating lease agreement, the term of which began in June 2015 and terminates in December 2022. Rent expense is recognized on a straight-line basis over the lease term. The maximum potential amount of future payments the Company could be required to make under this agreement is $3.0 million as of March 31, 2018. Additionally, Lexicon leases certain equipment under operating leases. Legal Proceedings. Lexicon is from time to time party to claims and legal proceedings that arise in the normal course of its business and that it believes will not have, individually or in the aggregate, a material adverse effect on its results of operations, financial condition or liquidity.

Collaboration and License Agreements

3 Months Ended

Mar. 31, 2018

Collaboration and License Agreements [Abstract]

Collaborative Arrangement Disclosure

Collaboration and License Agreements

Lexicon has derived substantially all of its revenues from drug discovery and development collaborations, target validation collaborations for the development and, in some cases, analysis of the physiological effects of genes altered in knockout mice, product sales, government grants and contracts, technology licenses, subscriptions to its databases and compound library sales.

Sanofi. In November 2015, Lexicon entered into a Collaboration and License Agreement, which was subsequently amended in July 2017 (collectively, the “Sanofi Agreement”), with Sanofi for the worldwide development of Lexicon’s diabetes drug candidate sotagliflozin. In December 2016, Sanofi terminated its rights under the Sanofi Agreement with respect to Japan.

Under the Sanofi Agreement, Lexicon has granted Sanofi an exclusive, worldwide (excluding Japan), royalty-bearing right and license under its patent rights and know-how to develop, manufacture and commercialize sotagliflozin. Subject to specified exceptions, neither party may (a) perform clinical development activities relating to any other compound which inhibits sodium-glucose cotransporters type 1 or type 2 or (b) commercialize any such compounds in the United States, countries of the European Union and certain other specified countries, in each case during the royalty terms applicable in such countries. Among the specified exceptions is a right Lexicon retained to pursue the development of its LX2761 drug candidate, with respect to which Lexicon granted Sanofi certain rights of first negotiation specified in the Sanofi Agreement.

Under the Sanofi Agreement, Sanofi paid Lexicon an upfront payment of $300 million. In addition, Lexicon is eligible to receive from Sanofi (a) up to an aggregate of $110 million upon the achievement of four development milestones relating to the results of certain Phase 3 clinical trials of sotagliflozin in type 2 diabetes patients, (b) up to an aggregate of $220 million upon the achievement of four regulatory milestones relating to the first commercial sale following regulatory approval of sotagliflozin for type 1 and type 2 diabetes, respectively, in each of the United States and Europe, of which two milestones representing the substantial majority of such aggregate amount relate to type 2 diabetes and the remaining two milestones relate to type 1 diabetes, (c) $100 million upon the achievement of a milestone based on the results of either of two outcomes studies in type 2 diabetes patients, the completion of which would likely occur after initial regulatory approval of sotagliflozin in type 2 diabetes, and (d) up to an aggregate of $990 million upon the achievement of six commercial milestones that will be achieved upon reaching specified levels of sales. The Company believes that each of the development and regulatory milestones under the Sanofi Agreement is substantive. Due to the uncertainty surrounding the achievement of the future development and regulatory milestones, these payments are deemed constrained and will not be recognized as revenue unless and until the constraint is resolved. Commercial milestones will be accounted for as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria were met. Lexicon is also entitled to tiered, escalating royalties ranging from low double digit percentages to forty percent of net sales of sotagliflozin, based on indication and territory, with royalties for the higher band of such range attributable to net sales for type 1 diabetes in the United States, and subject in each case to customary royalty reduction provisions.

Lexicon will continue to be responsible for all clinical development activities relating to type 1 diabetes and has exercised an exclusive option to co-promote and have a significant role, in collaboration with Sanofi, in the commercialization of sotagliflozin for the treatment of type 1 diabetes in the United States. Under the terms of its exercised co-promotion option, Lexicon will fund forty percent of the commercialization costs relating to such co-promotion activities. Sanofi will be responsible for all clinical development and commercialization of sotagliflozin for the treatment of type 2 diabetes worldwide and will be solely responsible for the commercialization of sotagliflozin for the treatment of type 1 diabetes outside the United States. Lexicon will share in the funding of a portion of the planned type 2 diabetes development costs over the first three years of the collaboration, up to an aggregate of $100 million. Sanofi will book sales worldwide in all indications.

The parties are responsible for using commercially reasonable efforts to perform their development and commercialization obligations pursuant to mutually approved development and commercialization plans.

The parties’ activities under the Sanofi Agreement are governed by a joint steering committee and certain other governance committees which reflect equal or other appropriate representation from both parties. If the applicable governance committee is not able to make a decision by consensus and the parties are not able to resolve the issue through escalation to specified senior executive officers of the parties, then Sanofi will have final decision-making authority, subject to limitations specified in the Sanofi Agreement.

The Sanofi Agreement will expire upon the expiration of all applicable royalty terms for all licensed products in all countries. The royalty term for each licensed product in each country is the period commencing on the effective date of the Sanofi Agreement and ending on the latest of expiration of specified patent coverage, expiration of specified regulatory exclusivity and 10 years following the first commercial sale in the applicable country. Either party may terminate the Sanofi Agreement in the event of an uncured material breach by the other party. Prior to completion of the core development activities for type 2 diabetes specified in the development plan, Sanofi may terminate the Sanofi Agreement on a country-by-country and licensed product-by-licensed product basis, in the event of (a) notification of a material safety issue relating to the licensed product or the class of sodium-glucose cotransporters type 1 or type 2 inhibitors resulting in a recommendation or requirement that Lexicon or Sanofi cease development, (b) failure to achieve positive results with respect to certain clinical trial results, (c) the occurrence of specified fundamental adverse events or (d) the exploitation of the licensed product infringing third party intellectual property rights in specified major markets and Sanofi is unable to obtain a license to such third party intellectual property rights.

The Company considered the following as its performance obligations with respect to the revenue recognition of the $300 million upfront payment:

• The exclusive worldwide license granted to Sanofi to develop and commercialize sotagliflozin;

• The development services Lexicon is performing for sotagliflozin relating to type 1 diabetes; and

• The funding Lexicon will provide for development relating to type 2 diabetes.

The Company determined that the license had stand-alone value because it is an exclusive license that gives Sanofi the right to develop and commercialize sotagliflozin or to sublicense its rights. In addition, sotagliflozin is currently in development and it is possible that Sanofi or another third party could conduct clinical trials without assistance from Lexicon. As a result, the Company considers the license and the development services under the Sanofi Agreement to be separate performance obligations. The Company recognized the portion of the transaction price allocated to the license immediately because Lexicon delivered the license and earned the revenue at the inception of the arrangement. The Company is recognizing as revenue the amount allocated to the development services for type 1 diabetes and the obligation to provide funding for development services for type 2 diabetes over the period of time Lexicon performs services or provides funding, currently expected to be through 2020.

The Company determined that the initial transaction price was the $300 million upfront payment because it was the only payment that was fixed and determinable at the inception of the arrangement. There was considerable uncertainty at the date of the agreement as to whether Lexicon would earn milestone payments or royalty payments. As such, the Company did not include those payments in the transaction price. The Company allocated the transaction price based on the relative best estimate of selling price of each performance obligation. The Company estimated the selling price of the license deliverable by applying a probability-based income approach utilizing an appropriate discount rate. The significant inputs the Company used to determine the projected income of the license included: exercising the option to co-promote, estimated future product sales, estimated cost of goods sold, estimated operating expenses, income taxes, and an appropriate discount rate. The Company estimated the selling price of the development services for type 1 diabetes by using internal estimates of the cost to hire third parties to perform the services over the expected period to perform the development. The Company estimated the obligation to provide funding for type 2 diabetes by using internal estimates of the expected cash flows and timing for $100 million in funding.

As a result of the allocation, the Company recognized $126.8 million of the $300 million upfront payment for the license in 2015. The Company is recognizing the $113.8 million allocated to the development services performance obligation and the $59.4 million allocated to the funding performance obligation over the estimated period of performance as the development and funding occurs. Milestone payments that are contingent upon the achievement of a substantive milestone are deemed constrained. If or when the constraint is determined to be resolved, the Company will re-evaluate the overall transaction price and recognize an adjustment on a cumulative catch-up basis in the period that the adjustment was evaluated. During the three months ended March 31, 2018, there has not been an adjustment to the transaction price. Revenue recognized under the Sanofi Agreement was $19.1 million and $17.0 million for the three months ended March 31, 2018 and 2017, respectively.

Ipsen. In October 2014, Lexicon entered into a License and Collaboration Agreement, which was subsequently amended in March 2015 (collectively, the “Ipsen Agreement”), with Ipsen for the development and commercialization of XERMELO outside of the United States and Japan (the “Licensed Territory”).

Under the Ipsen Agreement, Lexicon granted Ipsen an exclusive, royalty-bearing right and license under its patent rights and know-how to commercialize XERMELO in the Licensed Territory. Ipsen is responsible for using diligent efforts to commercialize XERMELO in the Licensed Territory pursuant to a mutually approved commercialization plan. Subject to certain exceptions, Lexicon was responsible for conducting clinical trials required to obtain regulatory approval for XERMELO for carcinoid syndrome in the European Union, including those contemplated by a mutually approved initial development plan, and has the first right to conduct most other clinical trials of XERMELO. Lexicon was responsible for the costs of all clinical trials contemplated by the initial development plan. The costs of additional clinical trials will be allocated between the parties based on the nature of such clinical trials. Under the Ipsen Agreement, Ipsen has paid Lexicon an aggregate of $43.7 million through March 31, 2018, consisting of $24.5 million in upfront payments and a $6.4 million milestone payment upon the acceptance of the filing submitted by Ipsen to the European Medicines Agency for XERMELO as an adjunct to somatostatin analog therapy for the long-term treatment of carcinoid syndrome, a $5.1 million milestone upon Ipsen’s receipt of approval from the European Commission for the marketing of XERMELO in all member states of the European Union, Norway and Iceland, a $3.84 million milestone upon Ipsen’s first commercial sale in Germany, and a $3.84 million milestone upon Ipsen’s first commercial sale in the United Kingdom. In addition, Lexicon is eligible to receive from Ipsen (a) up to an aggregate of approximately $13.1 million upon the achievement of specified regulatory and commercial launch milestones and (b) up to an aggregate of €72 million upon the achievement of specified sales milestones. Milestone payments that are contingent upon the achievement of a substantive milestone are deemed constrained. Lexicon is also entitled to tiered, escalating royalties ranging from low twenties to mid-thirties percentages of net sales of XERMELO in the Licensed Territory, subject to a credit for amounts previously paid to Lexicon by Ipsen for the manufacture and supply of such units of XERMELO. Lexicon and Ipsen have entered into a commercial supply agreement pursuant to which Lexicon will supply Ipsen’s commercial requirements of XERMELO, and Ipsen pays an agreed upon transfer price for such commercial supply.

The Company considered the following as its performance obligations with respect to the revenue recognition of the $24.5 million upfront payments:


•	The exclusive license granted to Ipsen to develop and commercialize XERMELO in the Licensed Territory;

•The development services Lexicon is performing for XERMELO;


•	The obligation to participate in committees which govern the development of XERMELO until commercialization; and

•The obligation to supply commercial supply of XERMELO, under a commercial supply agreement.

The Company determined that the license had stand-alone value because it is an exclusive license that gives Ipsen the right to develop and commercialize XERMELO or to sublicense its rights. In addition, at the time of the agreement, it would have been possible for Ipsen or another third party to conduct clinical trials without assistance from Lexicon. As a result, the Company considers the license and the development services under the Ipsen Agreement to be separate performance obligations. The Company recognized the portion of the transaction price to the license immediately because Lexicon delivered the license and earned the revenue at the inception of the arrangement. The Company is recognizing as revenue the amount allocated to the development services and the obligation to participate in committees over the period of time Lexicon performs services, currently expected to be complete in 2018.

The Company determined the commercial supply agreement is a contingent deliverable at the onset of the Agreement. There was inherent uncertainty in obtaining regulatory approval at the time of the agreement, thus, making the applicability of the commercial supply agreement outside the control of Lexicon and Ipsen. As a result, the Company has determined the commercial supply agreement does not meet the definition of a performance obligation that needs to be accounted for at the inception of the arrangement. The Company has also determined that there is no significant and incremental discount related to the commercial supply agreement that should be accounted for at the inception of the arrangement.

The Company determined that the initial transaction price was the $24.5 million upfront payments because they were the only payments that were fixed and determinable at the inception of the arrangement. There was considerable uncertainty at the date of the agreement as to whether Lexicon would earn milestone payments, royalty payments or payments for finished drug product. As such, the Company did not include those payments in the transaction price. The Company allocated the transaction price based on the relative best estimate of selling price of each performance obligation. The Company estimated the selling price of the license deliverable by applying a probability-based income approach utilizing an appropriate discount rate. The significant inputs the Company used to determine the projected income of the license included: estimated future product sales, estimated cost of goods sold, estimated operating expenses, income taxes, and an appropriate discount rate. The Company estimated the selling price of the development services by using internal estimates of the cost to hire third parties to perform the services over the expected period to perform the development. The Company estimated the selling price of the obligation to participate in committees by using internal estimates of the number of internal hours and salary and benefits costs to perform these services.

As a result of the allocation, the Company recognized $21.2 million of the $24.5 million upfront payments for the license in 2014, and an additional $1.4 million in 2015 upon entering into the amendment. The Company is recognizing the $1.7 million allocated to the development services performance obligation over the estimated period of performance as development occurs, and is recognizing the $0.1 million allocated to the committee participation performance obligation ratably over the estimated period of performance. Milestone payments that are contingent upon the achievement of a substantive milestone are deemed constrained. If or when the constraint is determined to be resolved, the Company will re-evaluate the overall transaction price and recognize an adjustment on a cumulative catch-up basis in the period that the adjustment was evaluated. During the three months ended March 31, 2018, there has not been an adjustment to the transaction price. Revenue recognized under the Agreement was $0.3 million and $0.5 million for the three months ended March 31, 2018 and 2017, respectively.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2018
Summary of Significant Accounting Policies [Abstract]
Consolidation, Policy [Policy Text Block]	The accompanying consolidated financial statements include the accounts of Lexicon and its wholly-owned subsidiaries. Intercompany transactions and balances are eliminated in consolidation.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates: The preparation of financial statements in conformity with U. S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the period. Actual results could differ from those estimates.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash, Cash Equivalents and Short-Term Investments: Lexicon considers all highly-liquid investments with original maturities of three months or less to be cash equivalents. As of March 31, 2018 and December 31, 2017, short-term investments consist of U.S. treasury bills and corporate debt securities. The Company’s short-term investments are classified as available-for-sale securities and are carried at fair value, based on quoted market prices of the securities. The Company views its available-for-sale securities as available for use in current operations regardless of the stated maturity date of the security. Unrealized gains and losses on such securities are reported as a separate component of stockholders’ equity. Net realized gains and losses, interest and dividends are included in interest income. The cost of securities sold is based on the specific identification method.
Trade and Other Accounts Receivable, Policy [Policy Text Block]	Accounts Receivable: Lexicon records trade accounts receivable in the normal course of business related to the sale of products or services. Write-offs are evaluated on a case by case basis.
Inventory, Policy [Policy Text Block]	Inventory: Inventory is comprised of the Company’s approved product, XERMELO. Inventories are determined at the lower of cost or market value with cost determined under the specific identification method and may consist of raw materials, work in process and finished goods.
Concentration Risk Disclosure [Text Block]	Concentration of Credit Risk: Lexicon’s cash equivalents, investments and accounts receivable represent potential concentrations of credit risk. The Company attempts to minimize potential concentrations of risk in cash equivalents and investments by placing investments in high-quality financial instruments. The Company’s accounts receivable are unsecured and are concentrated in pharmaceutical and biotechnology companies located in Europe and the United States. The Company has not experienced any significant credit losses to date.
Segment Reporting, Policy [Policy Text Block]	Segment Information and Significant Customers: Lexicon operates in one business segment, which primarily focuses on the discovery, development and commercialization of pharmaceutical products for the treatment of human disease. Substantially all of the Company’s revenues have been derived from drug discovery alliances, target validation collaborations for the development and, in some cases, analysis of the physiological effects of genes altered in knockout mice, technology licenses, subscriptions to its databases, product sales, government grants and contracts and compound library sales.
Property, Plant and Equipment, Policy [Policy Text Block]	Property and Equipment: Property and equipment that is held and used is carried at cost and depreciated using the straight-line method over the estimated useful life of the assets which ranges from three to 40 years. Maintenance, repairs and minor replacements are charged to expense as incurred. Leasehold improvements are amortized over the shorter of the estimated useful life or the remaining lease term. Significant renewals and betterments are capitalized.
Goodwill and Intangible Assets, Intangible Assets, Indefinite-Lived, Policy [Policy Text Block]	Other Intangible Assets: Other intangible assets, net consist of in-process research and development acquired in business combinations, which are reported at fair value, less accumulated amortization. Intangible assets with finite lives are amortized using the straight-line method over their estimated useful lives.
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]	Impairment of Long-Lived Assets: Long-lived assets and certain identifiable intangible assets to be held and used are reviewed for impairment when events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by comparison of the carrying amount of an asset to future net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount that the carrying amount of the assets exceeds the fair value of the assets. Assets to be disposed of are reported at the lower of the carrying amount or fair value less costs to sell.
Impairment or Disposal of Long-Lived Assets, Including Intangible Assets, Policy [Policy Text Block]	Indefinite lived intangible assets are also tested annually for impairment and whenever indicators of impairment are present. When performing the impairment assessment, the Company first assesses qualitative factors to determine whether it is necessary to recalculate the fair value of its intangible assets. If management believes, as a result of the qualitative assessment, that it is more likely than not that the fair value of the intangible assets is less than its carrying amount, the Company calculates the asset’s fair value. If the carrying value of the asset exceeds its fair value, then the intangible asset is written down to its fair value. Goodwill Impairment: Goodwill is not amortized, but is tested at least annually for impairment at the reporting unit level. The Company has determined that the reporting unit is the single operating segment disclosed in its current financial statements. Impairment is the condition that exists when the carrying amount of goodwill exceeds its implied fair value. The first step in the impairment process is to determine the fair value of the reporting unit and then compare it to the carrying value, including goodwill. If the fair value exceeds the carrying value, no further action is required and no impairment loss is recognized. Additional impairment assessments may be performed on an interim basis if the Company encounters events or changes in circumstances that would indicate that, more likely than not, the carrying value of goodwill has been impaired.
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition: Product Revenues Product revenues consist of commercial sales of XERMELO in the United States and sales of bulk tablets of XERMELO to Ipsen Pharma SAS (“Ipsen”). Product revenues are recognized when the customer obtains control of the Company’s product, which occurs upon delivery to the customer. The Company recognizes product revenue net of applicable reserves for variable consideration, including allowances for customer credits, estimated rebates, chargebacks, discounts, returns, distribution service fees, and government rebates, such as Medicare Part D coverage gap reimbursements in the U.S. These estimates are based on the most likely amount method for relevant factors such as current contractual and statutory requirements, industry data and forecasted customer buying and payment patterns. The Company’s net product revenues reflect the Company’s best estimates of the amounts of consideration to which it is entitled based on the terms of the respective underlying contracts. Product shipping and handling costs are considered a fulfillment activity when control transfers to the Company’s customers and such costs are included in cost of sales. Collaborative Agreements Revenues under collaborative agreements include both license revenue and contract research revenue. The Company performs the following five steps in determining the amount of revenue to recognize as it fulfills its performance obligations under each of its agreements: (i) identify the contract(s) with a customer; (ii) identify the performance obligation in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligation in the contract, and (v) recognize revenue when (or as) the Company satisfies the performance obligation. The Company applies this five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company develops assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. At contract inception, the Company evaluates whether development milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal will not occur, the associated development milestone value is included in the transaction price. Development milestones that are not within the control of the Company or the licensee, including those requiring regulatory approval, are not considered probable of being achieved until those approvals are received. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue when (or as) the performance obligation is satisfied. At the end of each reporting period, the Company re-evaluates the probability of achievement of the development milestones and any related constraint, and if necessary, adjusts its estimates of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenues in the period of adjustment. In agreements in which a license to the Company’s intellectual property is determined distinct from other performance obligations identified in the agreement, the Company recognizes revenue when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For agreements that include sales-based royalties, including milestones based on a level of sales, the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). The Company may receive payments from its licensees based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these agreements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.
Cost of Sales, Policy [Policy Text Block]	Cost of Sales: Cost of sales consists of third-party manufacturing costs, freight and indirect overhead costs associated with sales of XERMELO. The Company began capitalizing inventory during the three months ended March 31, 2017 once the FDA approved XERMELO as the related costs were expected to be recoverable through the commercialization of the product. Costs incurred prior to approval of XERMELO have been recorded as research and development expense in the consolidated statements of comprehensive loss. As a result, cost of sales for approximately the next two years will reflect a lower average per unit cost of materials. Product shipping and handling costs are included in cost of sales. Cost of sales also includes the amortization of the in-process research and development intangible asset for XERMELO using the straight-line method over the estimated useful life of 14 years.
Research and Development Expense, Policy [Policy Text Block]	Research and Development Expenses: Research and development expenses consist of costs incurred for company-sponsored as well as collaborative research and development activities. These costs include direct and research-related overhead expenses and are expensed as incurred. Technology license fees for technologies that are utilized in research and development and have no alternative future use are expensed when incurred. Substantial portions of the Company’s preclinical and clinical trials are performed by third-party laboratories, medical centers, contract research organizations and other vendors. For preclinical studies, the Company accrues expenses based upon estimated percentage of work completed and the contract milestones remaining. For clinical studies, expenses are accrued based upon the number of patients enrolled and the duration of the study. The Company monitors patient enrollment, the progress of clinical studies and related activities to the extent possible through internal reviews of data reported to the Company by the vendors and clinical site visits. The Company’s estimates depend on the timeliness and accuracy of the data provided by the vendors regarding the status of each program and total program spending. The Company periodically evaluates the estimates to determine if adjustments are necessary or appropriate based on information it receives.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	Stock-Based Compensation: The Company recognizes compensation expense in its consolidated statements of comprehensive loss for share-based payments, including stock options and restricted stock units issued to employees, based on their fair values on the date of the grant, with the compensation expense recognized over the period in which an employee is required to provide service in exchange for the stock award. Stock-based compensation expense for awards without performance conditions is recognized on a straight-line basis. Stock-based compensation expense for awards with performance conditions is recognized over the period from the date the performance condition is determined to be probable of occurring through the time the applicable condition is met. The fair value of stock options is estimated at the date of grant using the Black-Scholes method. The Black-Scholes option-pricing model requires the input of subjective assumptions. Because the Company’s employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models do not necessarily provide a reliable single measure of the fair value of its employee stock options. For purposes of determining the fair value of stock options, the Company segregates its options into two homogeneous groups, based on exercise and post-vesting employment termination behaviors, resulting in a change in the assumptions used for expected option lives and forfeitures. Expected volatility is based on the historical volatility in the Company’s stock price.
Income Tax, Policy [Policy Text Block]	Income Taxes: The Tax Cuts and Jobs Act (the “2017 Tax Act”) was enacted on December 22, 2017. The 2017 Tax Act significantly changes U.S. corporate income tax laws, including reducing the U.S. corporate income tax rate from 35 percent to 21 percent beginning in 2018. At March 31, 2018, Lexicon has not completed the accounting for the tax effects of the 2017 Tax Act; however, an estimate of the effects on the existing deferred tax balances has been made, as further discussed below. Lexicon recognizes deferred tax liabilities and assets for the expected future tax consequences of events that have been recognized differently in the financial statements and tax returns. Under this method, deferred tax liabilities and assets are determined based on the difference between the financial statement carrying amounts and tax bases of liabilities and assets using enacted tax rates and laws in effect in the years in which the differences are expected to reverse. Accordingly, in 2017 Lexicon remeasured certain deferred tax assets and liabilities based on the newly enacted U.S. corporate income tax rate, which resulted in a decrease of $171.4 million. Lexicon will continue to make and refine calculations and estimates, which could potentially affect the measurement of the deferred tax balances or give rise to new deferred tax assets. Where the Company has not yet been able to make reasonable estimates of the impact of certain elements, the Company has not recorded any amounts related to those elements and has continued accounting for them in accordance with ASC 740 on the basis of the tax laws in effect immediately prior to the enactment of the 2017 Tax Act. Deferred tax assets are evaluated for realization based on a more-likely-than-not criteria in determining if a valuation allowance should be provided.
Earnings Per Share, Policy [Policy Text Block]	Net Loss per Common Share: Net loss per common share is computed using the weighted average number of shares of common stock outstanding. Shares associated with convertible debt, stock options and restricted stock units are not included because they are antidilutive.

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2018

Summary of Significant Accounting Policies [Abstract]

Inventory, Major Classes, Policy [Policy Text Block]



	As of March 31,		As of December 31,
	2018		2017
	(in thousands)
Raw materials	$	617	$	616
Work-in-process	131		149
Finished goods	1,364		1,183
Total inventory	$	2,112	$	1,948

Summary of Significant Accounting Policies Equity Incentive Awards (Tables)

3 Months Ended

Mar. 31, 2018

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Abstract]

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]



	Expected Volatility		Risk-free Interest Rate		Expected Term	Dividend Rate
March 31, 2018:
Employees	60	%	2.5	%	4	—	%
Officers and non-employee directors	63	%	2.8	%	8	—	%
March 31, 2017:
Employees	62	%	1.7	%	4	—	%
Officers and non-employee directors	71	%	2.3	%	8	—	%

Share-based Compensation, Stock Options, Activity [Table Text Block]



	Options		Weighted Average Exercise Price
	(in thousands)
Outstanding at December 31, 2017	4,961		$	11.17
Granted	1,321		9.69
Exercised	(3	)	7.35
Expired	(170	)	14.23
Forfeited	(75	)	12.38
Outstanding at March 31,2018	6,034		10.74
Exercisable at March 31, 2018	3,253		$	10.89

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]



	Shares		Weighted Average Grant Date Fair Value
	(in thousands)
Outstanding at December 31, 2017	946		$	10.50
Granted	872		9.79
Vested	(334	)	9.85
Forfeited	(51	)	10.98
Outstanding at March 31, 2018	1,433		$	10.20

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Measurements [Abstract]

Fair Value, by Balance Sheet Grouping [Table Text Block]



	Assets and Liabilities at Fair Value as of March 31, 2018
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets
Cash and cash equivalents	$	20,421	$	—	$	—	$	20,421
Short-term investments	213,985		27,866		—		241,851
Total cash and cash equivalents and investments	$	234,406	$	27,866	$	—	$	262,272



	Assets and Liabilities at Fair Value as of December 31, 2017
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets
Cash and cash equivalents	$	61,661	$	—	$	—	$	61,661
Short-term investments	222,148		26,979		—		249,127
Total cash and cash equivalents and investments	$	283,809	$	26,979	$	—	$	310,788

Cash and Cash Equivalents and Investments (Tables)

3 Months Ended

Mar. 31, 2018

Cash and Cash Equivalents and Investments [Abstract]

Schedule of Cash, Cash Equivalents and Short-term Investments [Table Text Block]



	As of March 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	20,421	$	—	$	—		$	20,421
Securities maturing within one year:
U.S. treasury securities	214,302		—		(317		)	213,985
Corporate debt securities	27,943		—		(77		)	27,866
Total short-term investments	$	242,245	$	—	$	(394	)	$	241,851
Total cash and cash equivalents and investments	$	262,666	$	—	$	(394	)	$	262,272

	As of December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	61,661	$	—	$	—		$	61,661
Securities maturing within one year:
U.S. treasury securities	222,316		—		(168		)	222,148
Corporate debt securities	27,033		—		(54		)	26,979
Total short-term investments	$	249,349	$	—	$	(222	)	$	249,127
Total cash and cash equivalents and investments	$	311,010	$	—	$	(222	)	$	310,788

Summary of Significant Accounting Policies Inventory (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Inventory, Raw Materials, Gross	$ 617	$ 616
Inventory, Work in Process, Gross	131	149
Inventory, Finished Goods, Gross	1,364	1,183
Inventory, Gross	$ 2,112	$ 1,948

Summary of Significant Accounting Policies Other Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Summary of Significant Accounting Policies [Abstract]
XERMELO Intangible Assets Finite Lived	$ 24,700
Amortization of Intangible Assets	400	$ 100
Deferred tax benefit	$ 0	$ (8,652)

Summary of Significant Accounting Policies Impairment of Long-lived Assets (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Summary of Significant Accounting Policies [Abstract]
Asset Impairment Charges	$ 0	$ 0

Summary of Significant Accounting Policies Goodwill (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Summary of Significant Accounting Policies [Abstract]
Goodwill, Impairment Loss	$ 0	$ 0

Summary of Significant Accounting Policies Stock-based Compensation Valuation (Details) - Equity Option [Member]	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, ExpectedVolatilityRate, Employees	60.00%	62.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Employee	2.50%	1.70%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Employees	4 years	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate, Employees	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Officers and Non-employee Directors	63.00%	71.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Officers and Non-employee Directors	2.80%	2.30%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Officers and Non-employee Directors	8 years	8 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate, Officers and Non-employee Directors	0.00%	0.00%

Summary of Significant Accounting Policies Stock-based Compensation Summary (Details 1) - $ / shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	6,034	4,961
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 10.74	$ 11.17
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	1,321
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 9.69
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	3
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 7.35
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	170
Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price	$ 14.23
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	75
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price	$ 12.38
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	3,253
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$ 10.89
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	1,433	946
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 10.20	$ 10.50
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	872
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 9.79
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	334
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 9.85
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	51
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 10.98

Summary of Significant Accounting Policies Income Tax (Details) $ in Millions	Dec. 31, 2017 USD ($)
Summary of Significant Accounting Policies [Abstract]
Deferred Tax Asset, remeasured	$ 171.4

Fair Value Measurements (Details 1) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value
Cash and Cash Equivalents	$ 20,421	$ 61,661
Short-term Investments	241,851	249,127
Total Cash and Cash Equivalents and Investments	262,272	310,788
Fair Value, Level 1
Fair Value
Cash and Cash Equivalents	20,421	61,661
Short-term Investments	213,985	222,148
Total Cash and Cash Equivalents and Investments	234,406	283,809
Fair Value, Level 2
Fair Value
Cash and Cash Equivalents	0	0
Short-term Investments	27,866	26,979
Total Cash and Cash Equivalents and Investments	27,866	26,979
Fair Value, Level 3
Fair Value
Cash and Cash Equivalents	0	0
Short-term Investments	0	0
Total Cash and Cash Equivalents and Investments	$ 0	$ 0

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References + Details

Fair Value Measurements (Details 2) $ in Thousands	3 Months Ended
Fair Value Measurements (Details 2) $ in Thousands	Mar. 31, 2017 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	$ 2,101

Cash and Cash Equivalents and Investments (Details 1) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents
Fair Value
Amortized Cost	$ 20,421	$ 61,661
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	20,421	61,661
U.S. Treasury Securities
Fair Value
Amortized Cost	214,302	222,316
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(317)	(168)
Estimated Fair Value	213,985	222,148
Corporate Debt Securities
Fair Value
Amortized Cost	27,943	27,033
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(77)	(54)
Estimated Fair Value	27,866	26,979
Total Short-term Investments
Fair Value
Amortized Cost	242,245	249,349
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(394)	(222)
Estimated Fair Value	241,851	249,127
Total Cash and Cash Equivalents and Investments
Fair Value
Amortized Cost	262,666	311,010
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(394)	(222)
Estimated Fair Value	$ 262,272	$ 310,788

Cash and Cash Equivalents and Investments (Details 2) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Investments [Line Items]
Realized Investment Gains (Losses)	$ 0	$ (7,000)

Debt Obligations (Details)	1 Months Ended
Debt Obligations (Details)	Dec. 31, 2017	Nov. 30, 2014 USD ($)	Apr. 30, 2004 USD ($)	Mar. 31, 2018 USD ($)	Dec. 18, 2017 USD ($)	Nov. 20, 2014 $ / shares
Debt Instrument [Line Items]
Debt Issuance Costs, Gross					$ 4,100,000
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net				$ 3,900,000
Proceeds from Convertible Debt		$ 87,500,000
Convertible Debt Instrument Interest Rate Stated Percentage				0.00%
Debt Instrument, Convertible, Conversion Ratio		118.4553
Debt Instrument, Convertible, Conversion Price \| $ / shares						$ 8.442
Debt Issuance Cost		$ 3,400,000
Unamortized Debt Issuance Expense				$ 1,800,000
Debt Instrument, Fair Value Disclosure				111,900,000
Buildings Collateral				59,200,000
Land Collateral				$ 2,700,000
Debt Instrument, Description	200000000
Mortgage Loans on Real Estate, New Mortgage Loans			$ 34,000,000
Debt Instrument, Interest Rate, Stated Percentage				8.23%
Debt Instrument, Face Amount					$ 150,000,000
Mortgage Loans on Real Estate, Carrying Amount of Mortgages				$ 13,500,000

Arrangements with Symphony Icon Inc (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended
	Mar. 31, 2017	Sep. 30, 2016	Apr. 30, 2015	Dec. 31, 2014	Mar. 31, 2018	Mar. 31, 2017	Jul. 30, 2012	Jul. 30, 2010	Jun. 15, 2007
Loss Contingencies [Line Items]
Holdings Contribution to Icon									$ 45,000
Lexicon Sold Shares to Holdings									1,092,946
Lexicon Received Cash from Holdings									$ 15,000
Lexicon Paid Holdings Cash								$ 10,000
Symphony Base Payment in Shares							1,891,074
Symphony Base Payment Obligation							$ 35,000
Symphony Contingent Payment Maximum								$ 45,000
Symphony Contingent Payment Percentage								50.00%
Symphony Regulatory Approval Payment								$ 15,000
Symphony Regulatory Approval Reduction Percentage								50.00%
Symphony Regulatory Approval Percentage Limit								50.00%
Symphony Payment in Stock Limitation								50.00%
Symphony Contingent Payment In Cash	$ 10,500	$ 3,200	$ 750	$ 5,800
Symphony Amendment Buyout		$ 21,000
Symphony Contingent Payment in Shares	659,905			666,111
Symphony Contingent Payment Total				$ 11,500
Symphony Fair Value of Base and Contingent Payments								$ 45,600
Symphony Base Payment Discount Rate								14.00%
Symphony Contingent Payment Discount Rate								18.00%
Increase in fair value of Symphony Icon, Inc. purchase liability					$ 0	$ 2,101

Commitments and Contingencies (Details) $ in Millions	Mar. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 3.0

Collaboration and License Agreements (Details) $ in Thousands, € in Millions	1 Months Ended						3 Months Ended				9 Months Ended		12 Months Ended
	Nov. 30, 2017 USD ($)	Oct. 31, 2017 USD ($)	Nov. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Oct. 31, 2014 USD ($)	Oct. 31, 2014 EUR (€)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Collaboration and License Agreements [Abstract]
Sanofi Upfront Payment			$ 300,000
Sanofi Development Milestones			110,000
Sanofi Regulatory Milestones			220,000
Sanofi Outcomes Study Milestone			100,000
Sanofi Sales Milestone Payments			990,000
Sanofi Commercialization Costs Funded by Lexicon Maximum Amount			100,000
Sanofi Revenue Allocated to License Deliverable			126,800
Sanofi Revenue Allocated to Development Deliverable			113,800
Sanofi Revenue Allocated to Funding Deliverable			$ 59,400
Sanofi Revenue Recognized							$ 19,100		$ 17,000
Ipsen Total Payments							43,700
Ipsen Maximum Regulatory And Commercial Milestones					$ 13,000
Ipsen Maximum Sales Milestones \| €						€ 72
Ipsen Total Upfront Payments				$ 24,500
Ipsen Milestone Payment										$ 6,400	$ 5,100	$ 6,400
Ipsen Milestone Payment Received	$ 3,840	$ 3,840						$ 5,100
Ipsen Revenue Allocated to License Deliverable													$ 1,400	$ 21,200
Ipsen Revenue Allocated to Development Deliverable					1,700
Ipsen Revenue Allocated to Committee Deliverable					$ 100
Ipsen Revenue Recognized							$ 300		$ 500