Accumulated Other Comprehensive Income (Loss) Reclassifications Out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 2,594	$ 10,494	$ (4,850)	$ (24,244)
Other Comprehensive Income before reclassifications	22,907	(20,123)	35,101	36,061
Amounts reclassified from accumulated other comprehensive income (loss)	(2,157)	275	(2,309)	525
Income tax expense	(7,968)	7,629	(12,566)	(14,067)
Total other comprehensive income (loss)	12,782	(12,219)	20,226	22,519
Ending Balance	15,376	(1,725)	15,376	(1,725)
Investment Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	25,282	22,935	18,512	(11,396)
Other Comprehensive Income before reclassifications	22,907	(20,123)	35,101	36,061
Amounts reclassified from accumulated other comprehensive income (loss)	(2,796)	(57)	(4,038)	(469)
Income tax expense	(7,725)	7,757	(11,907)	(13,684)
Total other comprehensive income (loss)	12,386	(12,423)	19,156	21,908
Ending Balance	37,668	10,512	37,668	10,512
Defined Benefit Pension and Postretirement Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(22,688)	(12,441)	(23,362)	(12,848)
Other Comprehensive Income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	639	332	1,729	994
Income tax expense	(243)	(128)	(659)	(383)
Total other comprehensive income (loss)	396	204	1,070	611
Ending Balance	$ (22,292)	$ (12,237)	$ (22,292)	$ (12,237)