Shareholders' Equity - Reconciliation of Outstanding Balance of Stock Options (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding at beginning	490,000	601,000	813,000
Options granted	0	0	0
Options exercised	(69,000)	(111,000)	(202,000)
Options forfeited or expired			(10,000)
Options, Outstanding at ending	421,000	490,000	601,000
Options, Exercisable at ending	421,000
Weighted Average Exercise Price, Outstanding at beginning	$ 17.73	$ 16.97	$ 15.44
Weighted Average Exercise Price, Exercised	9.64	13.61	10.48
Weighted Average Exercise Price, Forfeited or expired			24.35
Weighted Average Exercise Price, Outstanding at ending	19.06	17.73	16.97
Weighted Average Exercise Price, Exercisable at ending	19.06
Weighted Average Grant Date Fair Value, Outstanding at beginning	8.69	8.42	7.96
Weighted Average Grant Date Fair Value, Exercised	6.75	7.25	6.48
Weighted Average Grant Date Fair Value, Forfeited or expired			9.84
Weighted Average Grant Date Fair Value, Outstanding at ending	$ 9.01	$ 8.69	$ 8.42
Aggregate Intrinsic Value, Outstanding	$ 4,601
Aggregate Intrinsic Value, Exercisable	$ 4,601