Schedule of Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Net accumulated other comprehensive income:
Net unrealized gain on investment securities available-for-sale	$ 20,248		$ 20,533
Net actuarial loss on defined benefit post-retirement benefit plans	(1,437)		(1,499)
Net accumulated other comprehensive income	$ 18,811	$ 19,034	$ 19,034