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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding at beginning	402,000		421,000
Options, Granted	0	0	0	0
Options, Exercised	(40,000)		(59,000)
Options, Forfeited or expired	0		0
Options, Outstanding at ending	362,000		362,000
Options, Exercisable at ending	362,000		362,000
Weighted Average Exercise Price, Outstanding at beginning	$ 19.49		$ 19.06
Weighted Average Exercise Price, Granted	0		0
Weighted Average Exercise Price, Exercised	9.64		9.64
Weighted Average Exercise Price, Forfeited or expired	0		0
Weighted Average Exercise Price, Outstanding at ending	20.60		20.60
Weighted Average Exercise Price, Exercisable at ending	20.60		20.60
Weighted Average Grant Date Fair Value, Outstanding at beginning	9.13		9.01
Weighted Average Grant Date Fair Value, Granted	0		0
Weighted Average Grant Date Fair Value, Exercised	6.30		6.30
Weighted Average Grant Date Fair Value, Forfeited or expired	0		0
Weighted Average Grant Date Fair Value, Outstanding at ending	$ 9.45		$ 9.45
Aggregate Intrinsic Value, Outstanding	$ 7,071		$ 7,071
Aggregate Intrinsic Value, Exercisable	$ 7,071		$ 7,071