Bank Premises and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 6,492,000	$ 5,875,000	$ 5,604,000
Rental income for leases included in net occupancy expense	$ 1,703,000	$ 1,646,000	$ 1,687,000