Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2019
Summary of Significant Accounting Policies [Abstract]
Consolidation, Policy [Policy Text Block]	The accompanying condensed 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 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 September 30, 2019, short-term investments consisted of U.S. treasury bills. As of December 31, 2018, short-term investments consisted 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 [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 it is commercializing in the United States, XERMELO^®(telotristat ethyl). 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, short-term investments and accounts receivable represent potential concentrations of credit risk. The Company attempts to minimize potential concentrations of risk in cash equivalents and short-term 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.
Lessee, Leases [Policy Text Block]	Leases: Lexicon leases certain office space and equipment for use in operations. Lease expense is recognized on a straight-line basis over the lease term. Right-of-use assets and lease liabilities are recorded on the condensed consolidated balance sheet for leases with a term greater than one year and are recognized based on the present value of the lease payments over the lease term.
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, right-of-use assets for leases and finite lived intangible assets 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. See Note 9, Impairment of Intangible Asset, for additional information. 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. 9. Impairment of Intangible Asset In 2007, Lexicon entered into a series of related agreements providing for the financing of the clinical development of certain of its drug candidates (the “Programs”), including LX1031 and LX1033. Under the financing arrangement, Lexicon licensed to Symphony Icon, Inc. (“Symphony Icon”) the Company’s intellectual property rights relating to the Programs. In 2010, Lexicon exercised an exclusive purchase option to acquire all of the equity of Symphony Icon, thereby reacquiring the Programs. Intangible assets which were included in the Programs and related to in-process research and development (“IPR&D”) were recognized and considered to be indefinite-lived until the completion or abandonment of the associated research and development efforts. These indefinite‑lived assets are not amortized, but are tested for impairment on an annual basis, as well as between annual tests if there are changes in circumstances that would indicate a reduction in the fair value of the IPR&D projects to less than their respective carrying amounts. A deferred tax liability was recognized related to the tax impact of future amortization or possible impairments associated with the identified intangible assets, which are not deductible for tax purposes. The Company determined that a triggering event occurred upon execution of the Termination Agreement with Sanofi and the Company’s resulting decision to substantially reallocate resources from the development of certain programs, including LX1031 and LX1033 for irritable bowel syndrome, to the development of sotagliflozin. In connection with such triggering event, the Company determined that its LX1031 and LX1033 programs for irritable bowel syndrome, collectively an intangible asset, were considered to be impaired and recorded an impairment charge of $28.6 million to IPR&D and a related income tax benefit of $6.0 million in the condensed consolidated statements of comprehensive income (loss) during the three months ended September 30, 2019. The impairment reduced the remaining book value to zero.
Revenue [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 Goods and Service [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. 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 Payment Arrangement [Policy Text Block]	Stock-Based Compensation: The Company recognizes compensation expense in its condensed consolidated statements of comprehensive income (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. Historical data is used to estimate the expected option life for each group. Expected volatility is based on the historical volatility in the Company’s stock price.
Earnings Per Share, Policy [Policy Text Block]	Net Income (Loss) per Common Share: Net income (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 that could potentially dilute earnings per share in the future are not included in the computation of diluted earnings per share because they are antidilutive.