Schedule of Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Net accumulated other comprehensive income:
Net unrealized gain on investment securities available-for-sale	$ 14,065		$ 17,537
Net actuarial loss on defined benefit post-retirement benefit plans	(1,525)		(1,546)
Net accumulated other comprehensive income	$ 12,540	$ 15,991	$ 15,991