Agreements - Roche (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		15 Months Ended
	May 31, 2000	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Collaborative Agreements disclosures
Non-cash royalty receivable		$ 8,115		$ 8,115
Non-cash royalty revenue related to sale of future royalties		8,441	$ 6,503	22,873	$ 20,555
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		$ 23,700		23,700
Roche | ASU 2014-09 | Adjustments due to new guidance | Kadcyla
Collaborative Agreements disclosures
Non-cash royalty revenue related to sale of future royalties				$ 22,900		$ 20,600