Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Federal income tax, current	$ 8,934	$ 9,973	$ 9,916
State income tax, current	1,050	880	831
Income tax, current	9,984	10,853	10,747
Federal income tax, deferred	1,363	2,372	293
State income tax, deferred	99	212	(4)
Income tax, deferred	1,462	2,584	289
Total income tax expense	$ 11,446	$ 13,437	$ 11,036