Organization and Basis of Presentation - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Oct. 26, 2016 USD ($)
Accounting Policies [Abstract]
Number of operating segments | segment									1
Net loss	$ (19,632)	$ (13,962)	$ (12,612)	$ (20,539)	$ (19,826)	$ (19,921)	$ (16,680)	$ (18,669)	$ (66,745)	$ (75,096)	$ (73,673)
Net cash used in operating activities									(51,504)	$ (65,209)	$ (58,044)
Cash, cash equivalents and marketable securities	$ 45,300								$ 45,300
CRG Loan
Debt Instrument [Line Items]
Line of credit facility, additional advances limit												$ 45,000