Stock-Based Compensation - Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Options Outstanding
Beginning balance (in shares)	983,512
Granted (in shares)	82,580
Exercised (in shares)	(293,034)
Canceled (in shares)	(16,137)
Ending balance (in shares)	756,921	983,512
Exercisable at period end (in shares)	579,744
Weighted-Average Exercise Price per Share
Beginning balance (in dollars per share)	$ 40.62
Granted (in dollars per share)	77.54
Exercised (in dollars per share)	22.94
Canceled (in dollars per share)	65.32
Ending balance (in dollars per share)	47.84	$ 40.62
Exercisable (in dollars per share)	$ 42.09
Weighted-Average Remaining Contractual Life
Outstanding, weighted average remaining contractual life (in years)	4 years 11 months	4 years
Exercisable weighted average remaining contractual life (in years)	4 years 1 month
Aggregate Intrinsic Value
Beginning balance	$ 40,137
Granted	1,737
Exercised	22,165
Canceled	537
Ending balance	38,406	$ 40,137
Exercisable	$ 32,750