Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Jan. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Lease Agreements [Member]
Loss Contingencies [Line Items]
Total rent expense for operating leases				$ 100,000	$ 100,000	$ 400,000	$ 200,000
Carna License Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid		$ 900,000
CPF License Agreements [Member]
Loss Contingencies [Line Items]
Upfront payment paid	$ 7,000,000
Operating Lease Agreement To Sublease Office Space [Member] | Vancouver [Member]
Loss Contingencies [Line Items]
Operating lease agreement expiration date						Feb. 27, 2018
Collateralized restricted deposit	25,000			$ 25,000		$ 25,000
Operating Lease Agreement To Lease Office Space [Member] | San Francisco [Member]
Loss Contingencies [Line Items]
Operating lease agreement expiration date			Apr. 30, 2019
Maximum [Member] | Carna License Agreement [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment						$ 270,000,000
Maximum [Member] | CPF License Agreements [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment	2,000,000
Additional milestone payment payable	$ 319,500,000