Stock Based Compensation - Summary of Stock Option Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure Stock Based Compensation Stock Option Plan [Abstract]
Shares, Outstanding, Beginning balance	1,558,438
Shares, Granted	276,192
Shares, Exercised	(42,089)	(126,808)
Shares, Forfeited or expired	(15,389)
Shares, Outstanding, Ending balance	1,777,152
Shares, Exercisable at June 30, 2018	1,191,092
Aggregate Intrinsic Value, Outstanding at June 30, 2018	$ 9,902,605
Aggregate Intrinsic Value, Exercisable at June 30, 2018	$ 9,780,319
Weighted Average Remaining Contractual Term, Outstanding at June 30, 2018	6 years
Weighted Average Remaining Contractual Term, Exercisable at June 30, 2018	4 years 7 months 6 days
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 31.09
Weighted Average Exercise Price, Granted	37.60
Weighted Average Exercise Price, Exercised	21.72
Weighted Average Exercise Price, Forfeited or expired	33.17
Weighted Average Exercise Price, Outstanding, Ending balance	32.30
Weighted Average Exercise Price, Exercisable	$ 28.73