Arrangements with Symphony Icon, Inc. (Details) (USD $)	0 Months Ended	1 Months Ended	12 Months Ended
	Dec. 04, 2014	Oct. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 30, 2012	Jul. 30, 2010	Jun. 15, 2007
Loss Contingencies
Holdings Contribution To Icon								$ 45,000,000
Lexicon Sold Shares To Holdings								7,650,622
Lexicon Received Cash From Holdings								15,000,000
Lexicon Paid Holdings Cash							10,000,000
Symphony Fair Value Of Base And Contingent Payments							45,600,000
Symphony Base Payment Discount Rate							14.00%
Symphony Contingent Payment Discount Rate							18.00%
Symphony Base Payment In Shares						13,237,519
Symphony Base Payment Obligation						35,000,000
Symphony Contingent Payment Maximum							45,000,000
Symphony Contingent Payment Percentage							50.00%
Symphony Regulatory Approval Payment							15,000,000
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	5,800,000
Symphony Contingent Payment in Shares	4,662,780
Symphony Contingent Payment Total	11,500,000
Ipsen Upfront Payment		23,000,000
Increase (decrease) in fair value of Symphony Icon, Inc. purchase liability			$ 1,428,000	$ (2,210,000)	$ 9,887,000