Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended					12 Months Ended
	Jan. 31, 2017	Oct. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Lease Agreements [Member]
Loss Contingencies [Line Items]
Total rent expense						$ 500,000	$ 300,000	$ 100,000
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
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]
Additional milestone payment payable			$ 319,500,000
Maximum [Member] | CPF License Agreements [Member] | Subsequent Event [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment	$ 2,000,000