Stock-Based Compensation - Summary of Option Activity for 2006 Plan and the 2016 Plan (Detail) - 2006 Plan and 2016 Plan - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Number of Shares
Beginning balance (in shares)	4,719,784
Granted (in shares)	477,500
Forfeited (in shares)	(231,385)
Exercised (in shares)	(605,195)
Ending balance (in shares)	4,360,704	4,719,784
Exercisable (in shares)	3,292,006
Vested and expected to vest at end of period (in shares)	4,202,009
Weighted Average Exercise Price at Grant Date
Beginning balance (in dollars per share)	$ 10.03
Granted (in dollars per share)	18.80
Forfeited (in dollars per share)	14.01
Exercised (in dollars per share)	8.84
Ending balance (in dollars per share)	10.94	$ 10.03
Exercisable (in dollars per share)	9.80
Vested and expected to vest at end of period (in dollars per share)	$ 10.72
Weighted Average Remaining Term (Years)
Weighted Average Remaining Term	5 years 8 months 19 days	5 years 7 months 17 days
Exercisable	4 years 9 months 19 days
Vested and expected to vest at end of period	5 years 7 months 2 days
Aggregate Intrinsic Value
Beginning balance	$ 24,421
Exercised	4,937
Ending balance	35,364	$ 24,421
Exercisable	30,445
Vested and expected to vest at end of period	$ 35,005