Accumulated Other Comprehensive Loss, Net of Tax (Schedule of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale securities:
Net unrealized loss during the period	$ 68,116	$ 120,333	$ (58,792)
Reclassification for net gain included in net income	(8)	(29)	0
Total available-for-sale securities	68,108	120,304	(58,792)
Derivative instruments:
Net unrealized gain during the period	27,683	(6,672)	280
Reclassification adjustment for net loss included in net income	11,420	6,832	7,425
Total derivative instruments	39,103	160	7,705
Defined benefit pension and other postretirement benefit plans:
Current year actuarial loss	(5,262)	2,202	(9,600)
Reclassification adjustment for amortization of net loss included in net income	3,976	5,706	7,708
Total (gain) loss recognized in OCI	1,286	(7,908)	1,892
Available-for-sale securities:
Net unrealized loss during the period	(17,937)	(31,686)	15,365
Reclassification for net gain included in net income	(2)	(7)	0
Total securities available-for-sale	17,935	31,679	(15,365)
Derivative instruments:
Net unrealized gain during the period	(7,016)	1,727	(72)
Reclassification adjustment for net loss included in net income	(2,985)	(1,758)	(1,930)
Total derivative instruments	(10,001)	(31)	(2,002)
Defined benefit pension and other postretirement benefit plans:
Current year actuarial loss	1,375	(580)	2,478
Reclassification adjustment for amortization of net loss included in net income	(1,036)	(1,502)	(1,983)
Total defined benefit pension and postretirement benefit plans	339	(2,082)	495
Available-for-sale securities:
Net unrealized loss during the period	50,179	88,647	(43,427)
Reclassification for net gain included in net income	(6)	(22)	0
Total available-for-sale securities	50,173	88,625	(43,427)
Derivative instruments:
Net unrealized gain during the period	20,667	(4,945)	208
Reclassification adjustment for net loss included in net income	8,435	5,074	5,495
Total derivative instruments	29,102	129	5,703
Defined benefit pension and other postretirement benefit plans:
Current year actuarial loss	(3,887)	1,622	(7,122)
Reclassification adjustment for amortization of net loss included in net income	2,940	4,204	5,725
Total defined benefit pension and postretirement benefit plans	(947)	5,826	(1,397)
Other Comprehensive Income (Loss), Pre-Tax Amount	105,925	128,372	(52,979)
Other Comprehensive Income (Loss), Tax Benefit (Expense)	(27,597)	(33,792)	13,858
Other comprehensive (loss) income, net of tax	$ 78,328	$ 94,580	$ (39,121)