Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Beginning balance (in shares)	4,580,375	4,246,525	3,561,304
Granted (in shares)	1,304,238	1,454,626	1,035,459
Option assumed from acquisition (in shares)			221,759
Exercised (in shares)	(887,062)	(650,185)	(385,328)
Forfeited/cancelled (in shares)	(312,597)	(470,591)	(186,669)
Ending balance (in shares)	4,684,954	4,580,375	4,246,525
Vested and exercisable (in shares)	2,773,387
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 8.20	$ 5.99	$ 4.62
Granted (in dollars per share)	13.52	13.43	11.13
Options assumed from acquisition (in dollars per share)			1.65
Exercised (in dollars per share)	6.59	4.43	3.50
Forfeited/cancelled (in dollars per share)	12.79	9.65	8.33
Ending balance (in dollars per share)	9.68	$ 8.20	$ 5.99
Vested and exercisable (in dollars per share)	$ 7.18
Weighted Average Remaining Contractual Life (in years)
Weighted Average Remaining Contractual Life, Outstanding
Weighted Average Remaining Contractual Life, Vested and exercisable
Aggregate Intrinsic Value (in thousands)
Stock options aggregate intrinsic value, Exercised	$ 9,665	$ 6,409	$ 3,472
Stock options aggregate intrinsic value, Outstanding	42,247
Stock options aggregate intrinsic value, Exercisable	$ 31,944