Stock Based Compensation - Stock Based Compensation Stock Option Activity (Detail) - Employee Stock Option - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of options, outstanding, beginning balance (in shares)	259,563
Number of options, granted (in shares)	0
Number of options, exercised (in shares)	(97,088)
Number of options, forfeited (in shares)	0
Number of options, outstanding, ending balance (in shares)	162,475	259,563
Number of options, vested and exercisable at December 31, 2017 (in shares)	162,475
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average exercise price, outstanding, beginning balance (in dollars per share)	$ 18.03
Weighted-average exercise price, granted (in dollars per share)	0.00
Weighted-average exercise price, exercised (in dollars per share)	14.39
Weighted-average exercise price, forfeited (in dollars per share)	0.00
Weighted-average exercise price, outstanding, ending balance (in dollars per share)	20.21	$ 18.03
Weighted average exercise price, vested and exercisable at December 31, 2017 (in dollars per share)	$ 20.21
Aggregate intrinsic value, outstanding	$ 5,267	$ 10,985
Aggregate intrinsic value, exercised	$ 4,446	$ 23,027	$ 12,911
Weighted-average remaining contractual life, outstanding, ending balance	2 years 2 months 27 days	2 years 9 months 3 days
Aggregate intrinsic value, vested and exercisable at December 31, 2017	$ 5,267
Weighted-average remaining contractual life, vested and exercisable at December 31, 2017	2 years 2 months 27 days