Other Comprehensive Income/Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Changes in accumulated other comprehensive loss components
Balance at the beginning of the period	$ (65,951)	$ (38,250)
Other comprehensive income, net of tax	2,491	3,158
Balance at the end of the period	(63,460)	(35,092)
Net unrealized (loss) gain on securities available-for-sale
Changes in accumulated other comprehensive loss components
Balance at the beginning of the period	4,686	(4,366)
Other comprehensive income, net of tax	1,993	2,993
Balance at the end of the period	6,679	(1,373)
Net actuarial loss on pension plans and other postretirement benefits
Changes in accumulated other comprehensive loss components
Balance at the beginning of the period	(67,476)	(30,600)
Other comprehensive income, net of tax	469	135
Balance at the end of the period	(67,007)	(30,465)
Prior service cost on pension plans and other postretirement benefits
Changes in accumulated other comprehensive loss components
Balance at the beginning of the period	(3,161)	(3,284)
Other comprehensive income, net of tax	29	30
Balance at the end of the period	$ (3,132)	$ (3,254)