Stock-Based Compensation - Summary of Stock Option Transactions and Related Information (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options Outstanding, Beginning Balance (in shares) | shares	748,371
Options, Granted (in shares) | shares	109,431
Options, Exercised (in shares) | shares	(273,026)
Options, Forfeited (in shares) | shares	(15,920)
Options Outstanding, Ending Balance (in shares) | shares	568,856
Options Exercisable, Ending Balance (in shares) | shares	316,295
Weighted Average Exercise Price, Outstanding Beginning Balance (in dollars per share) | $ / shares	$ 53.24
Weighted Average Exercise Price, Granted (in dollars per share) | $ / shares	107.49
Weighted Average Exercise Price, Exercised (in dollars per share) | $ / shares	46.46
Weighted Average Exercise Price, Forfeited (in dollars per share) | $ / shares	72.85
Weighted Average Exercise Price, Outstanding Ending Balance (in dollars per share) | $ / shares	67.14
Weighted Average Exercise Price, Exercisable Ending Balance (in dollars per share) | $ / shares	$ 55.20
Weighted Average Remaining Contractual Life - Years, Outstanding Ending Balance	7 years 6 months 29 days
Weighted Average Remaining Contractual Life - Years, Exercisable Ending Balance	5 years 10 months 10 days
Aggregate Intrinsic Value, Outstanding Ending Balance | $	$ 31,490
Aggregate Intrinsic Value, Exercisable Ending Balance | $	$ 21,287