Summary of Stock Appreciation Rights Activity (Detail) - Stock Appreciation Rights [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Grants outstanding at beginning of the year	170,000	170,000	170,000	170,000
Shares, Grants exercisable at end of the period	141,249	92,916	50,416
Shares, Grants vested and expected to vest at end of the period	167,813	170,000	170,000
Weighted Average Exercise Price per Share, Grants outstanding at beginning of the period	$ 18.18	$ 18.18	$ 18.18	$ 18.18
Weighted Average Exercise Price per Share, Grants exercisable at end of the period	17.59	17.80	17.48
Weighted Average Exercise Price per Share, Grants vested and expected to vest at end of the period	$ 18.29	$ 18.18	$ 18.18
Stock Appreciation Rights, Aggregate Intrinsic Value
SARs outstanding at December 31, 2015	$ 3,468
SARs exercisable at December 31, 2015	2,964
SARs vested and expected to vest at December 31, 2015	$ 3,406
Stock Appreciation Rights, Weighted Average Remaining Contractual Life
SARs outstanding at December 31, 2015	4 years 4 months 28 days
SARs exercisable at December 31, 2015	4 years 1 month 28 days
SARs vested and expected to vest at December 31, 2015	4 years 5 months 12 days