Share-based Compensation - Schedule of Compensation Expenses and Tax Benefits (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense (Benefit)	$ 875	$ 659	$ 911
Tax Benefit (Expense)	265	150	220
Director restricted stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense (Benefit)	70	56	56
Tax Benefit (Expense)	25	20	20
Director stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense (Benefit)		1	16
Tax Benefit (Expense)			6
Employee stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense (Benefit)	122	173	246
Tax Benefit (Expense)
Employee stock SARs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense (Benefit)	193	248	331
Tax Benefit (Expense)	68	87	116
Employee RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense (Benefit)	490	195
Tax Benefit (Expense)	172	68
Employee cash SARs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense (Benefit)		(70)	224
Tax Benefit (Expense)		$ (25)	$ 78