Accumulated Other Comprehensive Income Components of Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ (22,017)	$ (17,722)
Other comprehensive income before reclassifications	17,026	10,117
Reclassification adjustment from AOCI	(146)	(2,195)
Ending Balance	(5,137)	(9,800)
Unrealized Gains on Investment Securities Not Other-Than-Temporarily Impaired [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(6,499)	5,980
Other comprehensive income before reclassifications	17,026	9,992
Reclassification adjustment from AOCI	(616)	(1,661)
Ending Balance	9,911	14,311
Unrealized Non-Credit Losses on Other-Than-Temporarily Impaired Debt Securities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	458	1,349
Other comprehensive income before reclassifications	0	125
Reclassification adjustment from AOCI	0	(1,034)
Ending Balance	458	440
Unrealized Effective Portions of Losses on Forward-Starting Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(15)	(2,546)
Other comprehensive income before reclassifications	0	0
Reclassification adjustment from AOCI	4	34
Ending Balance	(11)	(2,512)
Unrecognized Pension and Postretirement Plan Income (Costs) [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(15,961)	(22,505)
Other comprehensive income before reclassifications	0	0
Reclassification adjustment from AOCI	466	466
Ending Balance	$ (15,495)	$ (22,039)