Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Dec. 31, 2015	Jan. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Rental expense			$ 400,000	$ 100,000	$ 100,000
Liabilities related to indemnification agreements	$ 0		$ 0	$ 0
South San Francisco California Sublease
Loss Contingencies [Line Items]
Lease expiration date			Jan. 31, 2017
South San Francisco California New Lease
Loss Contingencies [Line Items]
Lease expiration date	Apr. 30, 2021
Letter of credit expiration date	Dec. 31, 2016
South San Francisco California New Lease | Restricted Cash
Loss Contingencies [Line Items]
Letter of credit issued	$ 200,000
Westlake Village California [Member]
Loss Contingencies [Line Items]
Lease expiration date		Apr. 30, 2018
New York Lease
Loss Contingencies [Line Items]
Lease expiration date			Apr. 30, 2016