Accumulated Other Comprehensive Income Components of Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ (9,800)	$ (21,889)	$ (17,722)	$ (37,341)
Other comprehensive loss before reclassifications	(12,008)	13,313	(1,891)	29,579
Amounts reclassified from accumulated other comprehensive income (loss)	(1,069)	(585)	(3,264)	(1,399)
Ending Balance	(22,877)	(9,161)	(22,877)	(9,161)
Unrealized Gains on Investment Securities Not Other-Than-Temporarily Impaired [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	14,311	(13,577)	5,980	(27,510)
Other comprehensive loss before reclassifications	(12,008)	12,990	(2,016)	26,923
Amounts reclassified from accumulated other comprehensive income (loss)	(1,473)	7	(3,134)	7
Ending Balance	830	(580)	830	(580)
Unrealized Non-Credit Losses on Other-Than-Temporarily Impaired Debt Securities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	440	1,841	1,349	1,652
Other comprehensive loss before reclassifications	0	323	125	512
Amounts reclassified from accumulated other comprehensive income (loss)	(96)	(730)	(1,130)	(730)
Ending Balance	344	1,434	344	1,434
Unrealized Effective Portions of Losses on Forward-Starting Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2,512)	(2,648)	(2,546)	(2,682)
Other comprehensive loss before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	34	34	68	68
Ending Balance	(2,478)	(2,614)	(2,478)	(2,614)
Unrecognized Pension and Postretirement Plan Income (Costs) [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(22,039)	(7,505)	(22,505)	(8,801)
Other comprehensive loss before reclassifications	0	0	0	2,144
Amounts reclassified from accumulated other comprehensive income (loss)	466	104	932	(744)
Ending Balance	$ (21,573)	$ (7,401)	$ (21,573)	$ (7,401)