Summary of Information about Stock Appreciation Rights Outstanding (Detail) (SARs, USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of SARs Outstanding	548,482	1,232,808	4,338,250	4,147,391
Number of SARs Exercisable	445,238	966,045	3,468,805
Aggregate Intrinsic Value of SARs Outstanding as of Dec. 31, 2013	$ 4,305
Price Range One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant Price, lower range limit	$ 6.70
Grant Price, upper range limit	$ 8.76
Number of SARs Outstanding	73,311
Number of SARs Exercisable	73,311
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	3 years 11 months 5 days
Aggregate Intrinsic Value of SARs Outstanding as of Dec. 31, 2013	774
Price Range Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant Price, lower range limit	$ 9.25
Grant Price, upper range limit	$ 9.84
Number of SARs Outstanding	172,499
Number of SARs Exercisable	100,354
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	7 years 5 months 16 days
Aggregate Intrinsic Value of SARs Outstanding as of Dec. 31, 2013	1,590
Price Range Three
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant Price, lower range limit	$ 11.69
Grant Price, upper range limit	$ 17.31
Number of SARs Outstanding	302,672
Number of SARs Exercisable	271,573
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	6 years 1 month 17 days
Aggregate Intrinsic Value of SARs Outstanding as of Dec. 31, 2013	$ 1,941