Goodwill and Other Intangible Assets - Schedule of Change in Loan Servicing Rights (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Servicing Assets at Amortized Value [Line Items]
Balance at beginning of year	$ 12,900	$ 12,491	$ 11,722
Origination of loan servicing rights	12,039	4,483	4,182
Amortization expense	(4,955)	(4,074)	(3,413)
Balance at end of year	19,984	12,900	12,491
Balance at beginning of year	(2,670)	(1,163)	(612)
Impairment adjustment	(376)	(1,507)	(551)
Balance at end of year	(3,046)	(2,670)	(1,163)
Balance at end of year net of valuation allowance	$ 16,938	$ 10,230	$ 11,328