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Summary of Significant Accounting Policies - Contract Balances from Contracts with Customers - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Revenue recognized in the period from:
Probable milestone earned and paid	$ 500,000	$ 4,041,000
Deferred revenue	146,010,000	82,133,000	$ 80,802,000	$ 89,967,000
Revenue from contract with customer	8,584,000	19,815,000
Revenue recognized that was previously deferred	79,000	7,834,000
Milestone earned, included in accounts receivable	500,000
Milestone related
Revenue recognized in the period from:
Deferred revenue		1,000,000
Potential milestone payment		5,000,000
Clinical materials revenue
Revenue recognized in the period from:
Revenue from contract with customer		702,000
Upon shipment \| Clinical materials revenue
Revenue recognized in the period from:
Revenue recognized that was previously deferred		335,000
Kadcyla \| Royalty revenue
Revenue recognized in the period from:
Deferred revenue	65,200,000
Takeda
Revenue recognized in the period from:
Revenue from contract with customer		10,900,000
Takeda \| License Revenue
Revenue recognized in the period from:
Revenue from contract with customer		10,900,000
Revenue recognized that was previously deferred		6,900,000
Debiopharm
Revenue recognized in the period from:
Revenue recognized that was previously deferred		500,000
Other Collaborators \| Technological Improvements
Revenue recognized in the period from:
Amortization of deferred revenue	$ 79,000
Revenue recognized that was previously deferred		$ 101,000