Other Comprehensive Income/Loss (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Changes in accumulated other comprehensive loss components
Balance at the beginning of the period	$ (38,250)	$ (73,090)
Other comprehensive (loss) income, net of tax	(27,701)	34,840	2,571
Balance at the end of the period	(65,951)	(38,250)	(73,090)
Net unrealized (loss) gain on securities available-for-sale
Changes in accumulated other comprehensive loss components
Balance at the beginning of the period	(4,366)	7,451
Other comprehensive (loss) income, net of tax	9,052	(11,817)
Balance at the end of the period	4,686	(4,366)
Net actuarial loss on pension plans and other postretirement benefits
Changes in accumulated other comprehensive loss components
Balance at the beginning of the period	(30,600)	(77,115)
Other comprehensive (loss) income, net of tax	(36,876)	46,515
Balance at the end of the period	(67,476)	(30,600)
Prior service cost on pension plans and other postretirement benefits
Changes in accumulated other comprehensive loss components
Balance at the beginning of the period	(3,284)	(3,426)
Other comprehensive (loss) income, net of tax	123	142
Balance at the end of the period	$ (3,161)	$ (3,284)