Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 06, 2019
Cover page.
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Central Index Key	0000886163
Current Fiscal Year End Date	--12-31
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-33093
Entity Registrant Name	LIGAND PHARMACEUTICALS INCORPORATED
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0160744
Entity Address, Address Line One	3911 Sorrento Valley Boulevard, Suite 110
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	550-7500
Title of 12(b) Security	Common Stock , par value $0.001 per share
Trading Symbol	LGND
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		17,563,389