Summary of Significant Accounting Policies - Contract Balances (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jan. 02, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018
Changes in the Company’s contract assets and contract liabilities
Contract asset, Additions				$ 4,041,000
Contract asset, Deductions				(4,041,000)
Contract liabilities:
Deferred revenue, Deductions				(8,196,000)
Deferred revenue, Balance at End of Period	$ 89,967,000	$ 81,771,000		81,771,000
Revenues recognized from changes in contract asset and liability balances
Amounts included in contract liabilities at the beginning of the period		$ 1,321,000		13,196,000
Performance obligations satisfied in previous periods	$ 4,600,000
Milestone recognized as contract asset				4,041,000
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
Other 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				1,200,000
Upon shipment
Revenues recognized from changes in contract asset and liability balances
Deferred revenue recognized upon completion of performance obligations				$ 335,000
Adjustments due to new guidance | ASU 2014-09
Changes in the Company’s contract assets and contract liabilities
Contract asset, Additions			$ 5,000,000
Revenues recognized from changes in contract asset and liability balances
Milestone recognized as contract asset			$ 5,000,000