Summary of Interest Expense on Borrowings (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest Expense [Line Items]
Interest expense	$ 12,807	$ 13,162	$ 10,833
Reverse Repurchase Agreement
Interest Expense [Line Items]
Interest expense	8,573	11,207	9,116
Federal Home Loan Bank Advances
Interest Expense [Line Items]
Interest expense	4,071	1,776	1,513
Over Night Borrowings
Interest Expense [Line Items]
Interest expense	27	20	26
Capital Lease Obligations
Interest Expense [Line Items]
Interest expense	$ 136	$ 159	$ 178