Collaboration Revenue - Comparison of Reported Condensed Consolidated Cash Flows to Pro-forma Amounts (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Net loss	$ (27,787)	$ (28,018)	$ (55,706)	$ (53,492)
Deferred revenue			(7,863)	$ (6,029)
Previous Accounting in Effect [Member] \| ASU 2014-09 [Member] \| Pro Forma [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Net loss	$ (29,034)		(57,660)
Deferred revenue			$ (5,909)

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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