Summary of Significant Accounting Policies - Contract Balances (Details) - USD ($)		3 Months Ended		9 Months Ended
	Jan. 02, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Changes in the Company?s contract assets and contract liabilities
Contract asset, Additions				$ 500,000
Contract asset, Deductions				(5,000,000)
Contract Asset, Impact Of Netting		$ 5,000,000		5,000,000
Contract asset, Balance at End of Period		500,000		500,000
Contract liabilities:
Deferred revenue, Additions				706,000
Deferred revenue, Deductions				(13,368,000)
Contract Liabilities, Impact Of Netting		5,000,000		5,000,000
Deferred revenue, Balance at End of Period		82,305,000		82,305,000
Revenues recognized from changes in contract asset and liability balances
Amounts included in contract liabilities at the beginning of the period		172,000		13,368,000
Performance obligations satisfied in previous periods		500,000		500,000
Milestone recognized as contract asset				500,000
Revenue from contract with customer		10,928,000	$ 8,480,000	40,030,000	$ 75,999,000
Clinical material revenue		1,427,000	$ 1,248,000	2,465,000	$ 2,525,000
Takeda
Contract liabilities:
Deferred revenue, Deductions				(5,900,000)
Revenues recognized from changes in contract asset and liability balances
Amounts included in contract liabilities at the beginning of the period				10,900,000
Performance obligations satisfied in previous periods	$ 4,600,000
Deferred revenue recognized upon completion of performance obligations	400,000
Debiopharm and another collaborator
Revenues recognized from changes in contract asset and liability balances
Deferred revenue recognized upon completion of performance obligations				750,000
Other Collaborator | Technological Improvements
Revenues recognized from changes in contract asset and liability balances
Amortization of deferred revenue				1,300,000
Upon shipment | Other Collaborator
Revenues recognized from changes in contract asset and liability balances
Clinical material revenue				335,000
Adjustments due to new guidance | ASU 2014-09
Changes in the Company?s contract assets and contract liabilities
Contract asset, Additions		500,000		5,000,000
Revenues recognized from changes in contract asset and liability balances
Milestone recognized as contract asset		500,000		5,000,000
Pro forma as if previous accounting was in effect
Contract liabilities:
Deferred revenue, Balance at End of Period	$ 89,967,000
Pro forma as if previous accounting was in effect | ASU 2014-09
Revenues recognized from changes in contract asset and liability balances
Revenue from contract with customer		9,457,000		42,521,000
Clinical material revenue		$ 1,427,000		$ 2,465,000