Commitments and Contingencies - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Purchase commitments related to contract manufacturing, clinical development and certain other items	$ 63,300,000
Putative Securities Class Action [Member]
Loss Contingencies [Line Items]
Litigation matters, liabilities	0
Indemnification Obligation [Member]
Loss Contingencies [Line Items]
Litigation matters, liabilities	0	$ 0
Merger and Acquisition Related Claims [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	2,500,000
Securities Related Claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	2,500,000
Non-Securities Related Claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	$ 1,250,000