Annual report pursuant to Section 13 and 15(d)

Cover Page

Cover Page - USD ($)
$ in Billions
12 Months Ended
Dec. 31, 2020
Feb. 18, 2021
Jun. 30, 2020
Cover [Abstract]      
Amendment Flag false    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Entity Central Index Key 0000886163    
Current Fiscal Year End Date --12-31    
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2020    
Document Transition Report false    
Entity File Number 001-33093    
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 $.001 per share    
Trading Symbol LGND    
Security Exchange Name NASDAQ    
Entity Well-Known Seasoned Issuer Yes    
Entity Voluntary Filers No    
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    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 1.2
Entity Common Stock, Shares Outstanding   16,612,422