Fair Values of Assets and Liabilities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Random sample percentage of securities for each quarter	100.00%
Interest rate swaps transferred into Level 3 from Level 2	$ 461,000	$ 17,932,000
Corporate securities transferred from Level 3 to Level 2	0	11,965,000
Impaired loans considered to be credit risk of non-collection	100,000
Updated appraisal requirement floor	250,000
Other real estate book cost	11,300,000
Financial instrument of credit risk	200,000	200,000
Interest rate swap [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate swaps transferred into Level 3 from Level 2	$ 500,000	$ 4,500,000