Agreements - Roche (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	May 31, 2000	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Collaborative Agreements disclosures
Non-cash royalty receivable		$ 16,090
Non-cash royalty revenue related to sale of future royalties		7,190	$ 7,613
ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Non-cash royalty receivable					$ 8,900
Roche
Collaborative Agreements disclosures
Period in arrears to receive royalty reports and payments related to sales of Kadcyla	3 months
Roche | ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Non-cash royalty receivable		8,900
Roche | ASU 2014-09 | Adjustments due to new guidance | Kadcyla
Collaborative Agreements disclosures
Non-cash royalty revenue related to sale of future royalties		$ 7,200		$ 7,600