Agreements - Roche (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		15 Months Ended
	May 31, 2000	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Collaborative Agreements disclosures
Non-cash royalty receivable		$ 7,236		$ 7,236
Non-cash royalty revenue related to sale of future royalties		7,242	$ 6,439	14,432	$ 14,052
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		$ 16,100		16,100
Roche | ASU 2014-09 | Adjustments due to new guidance | Kadcyla
Collaborative Agreements disclosures
Non-cash royalty revenue related to sale of future royalties				$ 14,400		$ 14,100