Shareholders' Equity Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Beginning Balance	$ (22,017)	$ (17,722)	$ (37,341)
Other comprehensive income (loss) before reclassifications	(16,007)	(2,798)	20,402
Amounts reclassified from accumulated other comprehensive income (loss)	(425)	(3,953)	(783)
Reclassification adjustment for loss on derivative financial instruments included in net income	0	2,456	0
Ending Balance	(38,449)	(22,017)	(17,722)
Unrealized Gain (Losses) on Investment Securities Not Other-Than-Temporarily Impaired
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Beginning Balance	(6,499)	5,980	(27,510)
Other comprehensive income (loss) before reclassifications	(14,891)	(7,717)	33,734
Amounts reclassified from accumulated other comprehensive income (loss)	(1,657)	(4,762)	(244)
Reclassification adjustment for loss on derivative financial instruments included in net income		0
Ending Balance	(23,047)	(6,499)	5,980
Unrealized Non-Credit Gains (Losses) on Other-Than-Temporarily Impaired Debt Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Beginning Balance	458	1,349	1,652
Other comprehensive income (loss) before reclassifications	(185)	239	780
Amounts reclassified from accumulated other comprehensive income (loss)	0	(1,130)	(1,083)
Reclassification adjustment for loss on derivative financial instruments included in net income		0
Ending Balance	273	458	1,349
Unrealized Effective Portions of Losses on Forward-Starting Interest Rate Swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Beginning Balance	(15)	(2,546)	(2,682)
Other comprehensive income (loss) before reclassifications	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	15	75	136
Reclassification adjustment for loss on derivative financial instruments included in net income		2,456
Ending Balance	0	(15)	(2,546)
Unrecognized Pension and Postretirement Plan Income (Cost)
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Beginning Balance	(15,961)	(22,505)	(8,801)
Other comprehensive income (loss) before reclassifications	(931)	4,680	(14,112)
Amounts reclassified from accumulated other comprehensive income (loss)	1,217	1,864	408
Reclassification adjustment for loss on derivative financial instruments included in net income		0
Ending Balance	$ (15,675)	$ (15,961)	$ (22,505)