Summary of Stock Appreciation Rights Activity (Detail) - Stock Appreciation Rights [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Grants outstanding at beginning of the period	170,000	170,000	170,000
Shares, Exercised	(67,812)
Shares, Forfeited	(2,188)
Shares, Grants outstanding at end of the period	100,000	170,000	170,000
Shares, Grants exercisable at end of the period	100,000	141,249	92,916
Shares, Grants vested and expected to vest at end of the period	100,000	167,813	170,000
Weighted Average Exercise Price per Share, Grants outstanding at beginning of the period	$ 18.18	$ 18.18	$ 18.18
Weighted Average Exercise Price per Share, Exercised	10.08
Weighted Average Grant Date Fair Value per Share, Forfeited	10.08
Weighted Average Exercise Price per Share, Grants outstanding at end of the period	23.85	18.18	18.18
Weighted Average Exercise Price per Share, Grants exercisable at end of the period	23.85	17.59	17.80
Weighted Average Exercise Price per Share, Grants vested and expected to vest at end of the period	$ 23.85	$ 18.29	$ 18.18
Stock Appreciation Rights, Aggregate Intrinsic Value
SARs outstanding, exercisable and vested at December 31, 2016	$ 358,000
Stock Appreciation Rights, Weighted Average Remaining Contractual Life
SARs outstanding, exercisable and vested at December 31, 2016	5 years 10 months 6 days