Sale of Promacta License	9 Months Ended
Sep. 30, 2019
Discontinued Operations and Disposal Groups [Abstract]
Sale of Promacta License	Sale of Promacta LicenseOn March 5, 2019, we entered into an Asset Purchase Agreement (the “Asset Purchase Agreement”) with RPI Finance Trust (“RPI”), doing business as “Royalty Pharma”, who is not an affiliate. Under the Asset Purchase Agreement, we sold, transferred, assigned and conveyed to RPI, and RPI purchased, acquired and accepted from us, all of our rights, title and interest in and to the Purchased Assets, which include among other things the intellectual property and related know-how generated by us in connection with the license agreement (collectively, the “Purchased Assets”), dated December 29, 1994, by and between Novartis (as successor in interest to SmithKline Beecham Corporation) and Ligand, which allowed us to receive a royalty on net sales of Promacta. We concluded the sale does not qualify as a sale of a business, but as a sale of a non-financial asset. At the closing on March 6, 2019, RPI paid us $827.0 million in cash and we do not have any remaining performance obligations related to Novartis or RPI for Promacta. The carrying value of our Promacta asset as of March 6, 2019 was zero. Of the total cash proceeds from the sale, $14.2 million was recorded to revenue related to the Promacta royalty for the period between January 1, 2019 and March 6, 2019, and the remaining $812.8 million was recorded to income from operations in accordance with ASC 610-20, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets.

Sale of Promacta License

9 Months Ended

Sep. 30, 2019

Discontinued Operations and Disposal Groups [Abstract]

Sale of Promacta LicenseOn March 5, 2019, we entered into an Asset Purchase Agreement (the “Asset Purchase Agreement”) with RPI Finance Trust (“RPI”), doing business as “Royalty Pharma”, who is not an affiliate. Under the Asset Purchase Agreement, we sold, transferred, assigned and conveyed to RPI, and RPI purchased, acquired and accepted from us, all of our rights, title and interest in and to the Purchased Assets, which include among other things the intellectual property and related know-how generated by us in connection with the license agreement (collectively, the “Purchased Assets”), dated December 29, 1994, by and between Novartis (as successor in interest to SmithKline Beecham Corporation) and Ligand, which allowed us to receive a royalty on net sales of Promacta. We concluded the sale does not qualify as a sale of a business, but as a sale of a non-financial asset. At the closing on March 6, 2019, RPI paid us $827.0 million in cash and we do not have any remaining performance obligations related to Novartis or RPI for Promacta. The carrying value of our Promacta asset as of March 6, 2019 was zero. Of the total cash proceeds from the sale, $14.2 million was recorded to revenue related to the Promacta royalty for the period between January 1, 2019 and March 6, 2019, and the remaining $812.8 million was recorded to income from operations in accordance with ASC 610-20, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets.