Stock-based Compensation - Stock Option Activity (Detail) - Options - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Outstanding Options (in shares)
Balance at beginning of period (in shares)	3,506,529
Granted (in shares)	0
Forfeited (in shares)	(159,310)
Exercised (in shares)	(188,959)
Balance at end of period (in shares)	3,158,260	3,506,529
Vested (in shares)	3,149,795
Exercisable (in shares)	2,980,079
Weighted average exercise price per share (in dollars per share)
Balance at beginning of period (in dollars per share)	$ 7.32
Granted (in dollars per share)	0.00
Forfeited (in dollars per share)	5.38
Exercised (in dollars per share)	0.50
Balance at end of period (in dollars per share)	7.83	$ 7.32
Vested or expected to vest (in dollars per share)	7.83
Exercisable (in dollars per share)	$ 7.98
Weighted average remaining contractual life (in years)
Balance at beginning of period (in dollars per share)	4 years 4 months 29 days	5 years 15 days
Balance at end of period (in dollars per share)	4 years 4 months 29 days	5 years 15 days
Vested, exercisable, and expected to vest (in dollars per share)	4 years 4 months 27 days
Exercisable (in dollars per share)	4 years 2 months 26 days
Aggregate Intrinsic Value
Balance at beginning of period	$ 1,367
Balance at end of period	613	$ 1,367
Vested, exercisable, and expected to vest	613
Exercisable	$ 610