Fair Values of Assets and Liabilities - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2012	Dec. 31, 2011
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
Corporate securities transferred from Level 3 to Level 2	0	(4,520,000)	12,000,000		11,965,000
Impaired loans considered to be credit risk of non-collection	100,000			100,000
Updated appraisal requirement floor	250,000			250,000
Other real estate book cost	16,000,000			16,000,000
Sale of other real estate	1,200,000			1,200,000		6,800,000
Loss on sale of other real estate						300,000
Gain on sale of other real estate	600,000
Financial instrument of credit risk	$ 200,000			$ 200,000			$ 100,000