Summary of Information about Stock Appreciation Rights Outstanding (Detail) (SARs, USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of SARs Outstanding	1,232,808
Number of SARs Exercisable	966,045
Aggregate Intrinsic Value of SARs Outstanding as of Dec. 31, 2013	$ 12,046,835
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	$ 7.00
Number of SARs Outstanding	530,557
Number of SARs Exercisable	505,366
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	6 years 7 days
Aggregate Intrinsic Value of SARs Outstanding as of Dec. 31, 2013	6,322,045
Price Range Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant Price, lower range limit	$ 7.34
Grant Price, upper range limit	$ 8.76
Number of SARs Outstanding	139,602
Number of SARs Exercisable	130,288
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	4 years 11 months 23 days
Aggregate Intrinsic Value of SARs Outstanding as of Dec. 31, 2013	1,434,848
Price Range Three
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant Price, lower range limit	$ 9.50
Grant Price, upper range limit	$ 16.19
Number of SARs Outstanding	562,649
Number of SARs Exercisable	330,391
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	7 years 4 months 28 days
Aggregate Intrinsic Value of SARs Outstanding as of Dec. 31, 2013	$ 4,289,943