This item represents the change in fair value of the Symphony Icon, Inc. purchase liability. In connection with the acquisition of Symphony Icon, Lexicon made an initial estimate of the fair value of the liability for the associated based and contingent payments. Changes in this liability, based on the development of the programs and the time until such payments are expected to be made, are recorded in Lexicon's consolidated statements of operations.

No definition available.

Arrangements with Symphony Icon Inc (Details) (USD $)	3 Months Ended		6 Months Ended
Arrangements with Symphony Icon Inc (Details) (USD $)	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jul. 30, 2012	Jul. 30, 2010	Jun. 15, 2007
Loss Contingencies [Line Items]
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 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 fair value of base and contingent payments						45,600,000
Symphony base payment discount rate						14.00%
Symphony contingent payment discount rate						18.00%
Increase in fair value of Symphony Icon, Inc. purchase liability	$ 477,000	$ 2,162,000	$ 1,741,000	$ 4,243,000