Stock-Based Compensation Expense - Summary of Stock Option Activity (Detail) - Stock Options [Member] $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Shares
Outstanding, Beginning balance (in shares) | shares	4,580,375
Granted (in shares) | shares	1,266,238
Exercised (in shares) | shares	(670,533)
Forfeited/canceled (in shares) | shares	(134,812)
Outstanding, Ending balance (in shares) | shares	5,041,268
Vested and exercisable (in shares) | shares	2,642,121
Vested or expected to vest (in shares) | shares	4,544,979
Weighted Average Exercise Price
Outstanding, Beginning balance (in dollars per share) | $ / shares	$ 8.20
Granted (in dollars per share) | $ / shares	13.38
Exercised (in dollars per share) | $ / shares	6.13
Forfeited/canceled (in dollars per share) | $ / shares	12.41
Outstanding, Ending balance (in dollars per share) | $ / shares	9.66
Vested and exercisable (in dollars per share) | $ / shares	6.57
Vested and expected to vest (in dollars per share) | $ / shares	$ 9.27
Weighted Average Remaining Contractual Life (in years)
Outstanding	7 years 6 months
Vested and exercisable	6 years
Vested and expected to vest	7 years 1 month 6 days
Aggregate Intrinsic Value
Exercised (in dollars) | $	$ 7,572
Outstanding (in dollars) | $	36,564
Vested and exercisable (in dollars) | $	27,278
Vested and expected to vest (in dollars) | $	$ 34,726