Fair Values of Assets and Liabilities - Losses Realized on Assets Measured on Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Impaired loans	$ (3,890)	$ (7,148)	$ (7,352)	$ (28,075)
Other real estate owned	(366)	(88)	(523)	(4,185)
Total losses	$ (4,256)	$ (7,236)	$ (7,875)	$ (32,260)