Commitments and Contingencies - Additional Information (Detail) $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 29, 2016 $ / ft²	May 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Operating Leased Assets [Line Items]
Commencement date of lease		2015-09
Acquisition of leasehold improvements		$ 445		$ 445
Lease amendment commencement date	Jul. 01, 2016
Lease term	90 months
Lease extension term	5 years
Lease description			The lease term is 90 months and the Company has the right to extend the term for one period of five years.
Annual lease rate per square foot in first year of lease | $ / ft²	25
Annual lease rate per square foot in last year of lease | $ / ft²	30.50
Operating leases, rent expenses			$ 275	143
Research and development expense			$ 31,985	$ 12,554
Transition Agreement [Member]
Operating Leased Assets [Line Items]
Description of Transition Agreement			Pursuant to the terms of the Transition Agreement, Dr. McVicar will remain an employee of the Company as a Senior Advisor for a six-month period ending April 4, 2017 (the “Transition Period”) and for twelve months thereafter will receive his salary and medical benefits at the same rate in effect as of the date of the Transition Agreement.
Former Chief Scientific Officer [Member] | Transition Agreement [Member]
Operating Leased Assets [Line Items]
Research and development expense			$ 900
Former Chief Scientific Officer [Member] | Transition Agreement [Member] | Stock Options [Member]
Operating Leased Assets [Line Items]
Stock based compensation expense			$ 200