Accumulated Other Comprehensive Income Components of Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ 7,689	$ (22,877)	$ (22,017)	$ (17,722)
Other comprehensive loss before reclassifications	(3,580)	7,857	26,285	5,966
Amounts reclassified from accumulated other comprehensive income (loss)	382	(655)	223	(3,919)
Reclassification adjustment for loss on derivative financial instruments included in net income	0	2,456	0	2,456
Ending Balance	4,491	(13,219)	4,491	(13,219)
Unrealized Gains (Losses) on Investment Securities Not Other-Than-Temporarily Impaired
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	22,701	830	(6,499)	5,980
Other comprehensive loss before reclassifications	(3,580)	7,857	26,285	5,841
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	(1,124)	(666)	(4,258)
Reclassification adjustment for loss on derivative financial instruments included in net income		0		0
Ending Balance	19,120	7,563	19,120	7,563
Unrealized Non-Credit Gains (Losses) on Other-Than-Temporarily Impaired Debt Securities
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	458	344	458	1,349
Other comprehensive loss before reclassifications	0	0	0	125
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0	(1,130)
Reclassification adjustment for loss on derivative financial instruments included in net income		0		0
Ending Balance	458	344	458	344
Unrealized Effective Portions of Losses on Forward-Starting Interest Rate Swaps
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(7)	(2,478)	(15)	(2,546)
Other comprehensive loss before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	4	3	12	71
Reclassification adjustment for loss on derivative financial instruments included in net income		2,456		2,456
Ending Balance	(3)	(19)	(3)	(19)
Unrecognized Pension and Postretirement Plan Income (Costs)
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(15,463)	(21,573)	(15,961)	(22,505)
Other comprehensive loss before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	379	466	877	1,398
Reclassification adjustment for loss on derivative financial instruments included in net income		0		0
Ending Balance	$ (15,084)	$ (21,107)	$ (15,084)	$ (21,107)