Stock-Based Compensation - Reconciliation of Outstanding Balance of Stock Options (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding at beginning	503,000	513,000
Options, Granted	0	0	0
Options, Exercised	(13,000)	(23,000)
Options, Forfeited or expired	0	0
Options, Outstanding at ending	490,000	490,000
Options, Exercisable at ending	332,000	332,000
Options, Unvested at ending	158,000	158,000
Weighted Average Exercise Price, Outstanding at beginning	$ 28.89	$ 28.52
Weighted Average Exercise Price, Granted	0	0
Weighted Average Exercise Price, Exercised	14.99	12.77
Weighted Average Exercise Price, Forfeited or expired	0	0
Weighted Average Exercise Price, Outstanding at ending	29.26	29.26
Weighted Average Exercise Price, Exercisable at ending	28.88	28.88
Weighted Average Exercise Price, Unvested at ending	30.05	30.05
Weighted Average Grant Date Fair Value, Outstanding at beginning	13.26	13.10
Weighted Average Grant Date Fair Value, Granted	0	0
Weighted Average Grant Date Fair Value, Exercised	8.12	6.81
Weighted Average Grant Date Fair Value, Forfeited or expired	0	0
Weighted Average Grant Date Fair Value, Outstanding at ending	$ 13.40	$ 13.40
Aggregate Intrinsic Value, Outstanding	$ 7,414	$ 7,414
Aggregate Intrinsic Value, Exercisable	5,144	5,144
Aggregate Intrinsic Value, Unvested	$ 2,270	$ 2,270