Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2016	Feb. 09, 2017	Jun. 30, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	LIGAND PHARMACEUTICALS INC
Entity Central Index Key	0000886163
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Amendment Flag	false
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		20,919,894
Entity Public Float			$ 2.3
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes