Subsequent Event (Notes)	9 Months Ended
Sep. 30, 2015
Subsequent Event [Line Items]
Subsequent Events [Text Block]	Subsequent Event On November 5, 2015, Lexicon entered into a Collaboration and License Agreement (the “Sanofi Agreement”) with Sanofi for the worldwide development of Lexicon’s diabetes drug candidate sotagliflozin (LX4211). Under the Sanofi Agreement, Lexicon granted Sanofi an exclusive, worldwide, 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 will pay Lexicon an upfront payment of $300 million. In addition, Lexicon is eligible to receive from Sanofi (a) up to an aggregate of $430 million upon the achievement of specified development and regulatory milestones and (b) up to an aggregate of $990 million upon the achievement of specified sales milestones. 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. Royalties payable with respect to net sales of sotagliflozin for type 1 diabetes in the United States will also be reduced in the event Lexicon does not exercise its co-promotion option described below. Lexicon will continue to be responsible for all clinical development activities relating to type 1 diabetes and will retain 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. If Lexicon exercises its 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 next three years, 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 effectiveness of the Sanofi Agreement is contingent upon satisfaction of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the “HSR Act”).

Subsequent Event

On November 5, 2015, Lexicon entered into a Collaboration and License Agreement (the “Sanofi Agreement”) with Sanofi for the worldwide development of Lexicon’s diabetes drug candidate sotagliflozin (LX4211).

Under the Sanofi Agreement, Lexicon granted Sanofi an exclusive, worldwide, 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 will pay Lexicon an upfront payment of $300 million. In addition, Lexicon is eligible to receive from Sanofi (a) up to an aggregate of $430 million upon the achievement of specified development and regulatory milestones and (b) up to an aggregate of $990 million upon the achievement of specified sales milestones. 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. Royalties payable with respect to net sales of sotagliflozin for type 1 diabetes in the United States will also be reduced in the event Lexicon does not exercise its co-promotion option described below.

Lexicon will continue to be responsible for all clinical development activities relating to type 1 diabetes and will retain 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. If Lexicon exercises its 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 next three years, 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 effectiveness of the Sanofi Agreement is contingent upon satisfaction of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the “HSR Act”).