Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components of accumulated other comprehensive loss, net of related tax benefit/expense
Net unrealized gains on investment securities — available-for-sale, net of related tax expense of $2,301 at December 31, 2012, $1,796 at December 31, 2011 and $1,786 at December 31, 2010	$ 4,274	$ 3,336	$ 3,317
Pension and other postretirement benefits adjustment, net of related tax benefit of $19,058 at December 31, 2012, $15,435 at December 31, 2011 and $9,384 at December 31, 2010	(35,393)	(28,665)	(17,428)
Accumulated other comprehensive loss	$ (31,119)	$ (25,329)	$ (14,111)