Other Comprehensive Income - Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Net accumulated other comprehensive income:
Net unrealized gain on investment securities available-for-sale	$ 17,537	$ 20,533
Net actuarial loss on defined benefit post-retirement benefit plans	(1,546)	(1,499)
Net accumulated other comprehensive income	$ 15,991	$ 19,034