Stock-Based Compensation - Reconciliation of Outstanding Balance of Stock Options (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding at beginning	515,000
Options, Granted	0	0
Options, Exercised	(46,000)
Options, Forfeited or expired	0
Options, Outstanding at ending	469,000
Options, Exercisable at ending	302,000
Options, Unvested at ending	167,000
Weighted Average Exercise Price, Outstanding at beginning	$ 25.13
Weighted Average Exercise Price, Granted	0
Weighted Average Exercise Price, Exercised	12.30
Weighted Average Exercise Price, Forfeited or expired	0
Weighted Average Exercise Price, Outstanding at ending	26.38
Weighted Average Exercise Price, Exercisable at ending	24.10
Weighted Average Exercise Price, Unvested at ending	30.50
Weighted Average Grant Date Fair Value, Outstanding at beginning	11.64
Weighted Average Grant Date Fair Value, Granted	0
Weighted Average Grant Date Fair Value, Exercised	6.84
Weighted Average Grant Date Fair Value, Forfeited or expired	0
Weighted Average Grant Date Fair Value, Outstanding at ending	$ 12.10
Aggregate Intrinsic Value, Outstanding	$ 992
Aggregate Intrinsic Value, Exercisable	992
Aggregate Intrinsic Value, Unvested	$ 0