Accumulated Other Comprehensive Income Components of Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ (17,722)	$ (37,341)
Other comprehensive income before reclassifications	10,117	16,266
Amounts reclassified from accumulated other comprehensive income (loss)	(2,195)	(814)
Ending Balance	(9,800)	(21,889)
Unrealized Gains on Investment Securities Not Other-Than-Temporarily Impaired [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	5,980	(27,510)
Other comprehensive income before reclassifications	9,992	13,933
Amounts reclassified from accumulated other comprehensive income (loss)	(1,661)	0
Ending Balance	14,311	(13,577)
Unrealized Non-Credit Losses on Other-Than-Temporarily Impaired Debt Securities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	1,349	1,652
Other comprehensive income before reclassifications	125	189
Amounts reclassified from accumulated other comprehensive income (loss)	(1,034)	0
Ending Balance	440	1,841
Unrealized Effective Portions of Losses on Forward-Starting Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2,546)	(2,682)
Amounts reclassified from accumulated other comprehensive income (loss)	34	34
Ending Balance	(2,512)	(2,648)
Unrecognized Pension and Postretirement Plan Income (Costs) [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(22,505)	(8,801)
Other comprehensive income before reclassifications		2,144
Amounts reclassified from accumulated other comprehensive income (loss)	466	(848)
Ending Balance	$ (22,039)	$ (7,505)