Summary of Information about Stock Appreciation Rights Outstanding (Detail) (SARs, USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
SARs Outstanding	4,338,250
SARs Exercisable	3,468,805
Aggregate Intrinsic Value of SARs Outstanding at December 31, 2011	$ 10,994
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
SARs Outstanding	1,369,717
SARs Exercisable	1,008,742
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	7 years
Aggregate Intrinsic Value of SARs Outstanding at December 31, 2011	4,709
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	$ 7.34
SARs Outstanding	1,946,110
SARs Exercisable	1,946,110
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	2 years 7 months 6 days
Aggregate Intrinsic Value of SARs Outstanding at December 31, 2011	5,488
Price Range Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Price, lower range limit	$ 8.13
Grant Price, upper range limit	$ 8.76
SARs Outstanding	298,948
SARs Exercisable	271,134
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	6 years 1 month 6 days
Aggregate Intrinsic Value of SARs Outstanding at December 31, 2011	528
Price Range Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Price, lower range limit	$ 9.50
Grant Price, upper range limit	$ 12.15
SARs Outstanding	723,475
SARs Exercisable	242,819
Weighted Average Remaining Contractual Life of SARs Outstanding (in years)	8 years 1 month 6 days
Aggregate Intrinsic Value of SARs Outstanding at December 31, 2011	$ 269