Stock-based Compensation - Summary of Stock Option Activity for Employees and Nonemployees (Detail) - Employee and Nonemployee Stock Option [Member] - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option activity, shares outstanding, at beginning of period	5,574,179
Stock option activity, shares granted	1,880,200
Stock option activity, shares exercised	(15,686)
Stock option activity, shares canceled	(592,501)
Stock option activity, shares outstanding, at end of period	6,846,192	5,574,179
Stock option activity, options exercisable at end of period	3,553,381
Weighted average exercise price, options outstanding at beginning of period	$ 16.55
Weighted average exercise price, options granted	10.18
Weighted average exercise price, options exercised	5.39
Weighted average exercise price, option canceled	16.04
Weighted average exercise price, options outstanding at end of period	14.87	$ 16.55
Weighted average exercise price, options exercisable at end of period	$ 16.60
Weighted average remaining contractual life outstanding	7 years 6 months	7 years 8 months 12 days
Weighted average exercise price exercisable	6 years 2 months 12 days
Aggregate intrinsic value outstanding	$ 10,758	$ 12,178
Aggregate intrinsic value exercisable	$ 8,857