Accumulated Other Comprehensive Loss, Net of Tax (Schedule of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale and transferred securities:
Net unrealized loss during the period	$ (14,113)	$ (35,701)	$ 34,242
Reclassification for net gain included in net income	(414)	(609)	(5,499)
Net non-credit other-than-temporary impairment	149	110	1,145
Amortization of unrealized loss on securities transferred to held-to-maturity	0	37	60
Total available-for-sale and transferred securities	(14,378)	(36,163)	29,948
Derivative instruments:
Net unrealized gain during the period	1,331	(4,945)	(19,589)
Reclassification adjustment for net loss included in net income	8,020	8,965	8,100
Total derivative instruments	9,351	4,020	(11,489)
Defined benefit pension and other postretirement benefit plans:
Current year actuarial loss	(368)	(8,719)	(33,567)
Reclassification adjustment for amortization of net loss included in net income	7,126	6,161	2,921
Reclassification adjustment for prior service cost included in net income	14	73	73
Total defined benefit pension and postretirement benefit plans	6,772	(2,485)	(30,573)
Available-for-sale and transferred securities:
Net unrealized loss during the period	5,212	13,166	(12,469)
Reclassification for net gain included in net income	152	223	1,999
Net non-credit other-than-temporary impairment	(55)	(40)	(418)
Amortization of unrealized loss on securities transferred to held-to-maturity	0	(14)	(22)
Total available-for-sale and transferred securities	5,309	13,335	(10,910)
Derivative instruments:
Net unrealized gain during the period	(506)	1,809	7,083
Reclassification adjustment for net loss included in net income	(2,933)	(3,279)	(2,918)
Total derivative instruments	(3,439)	(1,470)	4,165
Defined benefit pension and other postretirement benefit plans:
Current year actuarial loss	136	3,219	12,238
Reclassification adjustment for amortization of net loss included in net income	(2,633)	(2,274)	(1,065)
Reclassification adjustment for prior service cost included in net income	(5)	(27)	(26)
Total defined benefit pension and postretirement benefit plans	(2,502)	918	11,147
Available-for-sale and transferred securities:
Net unrealized loss during the period	(8,901)	(22,535)	21,773
Reclassification for net gain included in net income	(262)	(386)	(3,500)
Net non-credit other-than-temporary impairment	94	70	727
Amortization of unrealized loss on securities transferred to held-to-maturity	0	23	38
Total available-for-sale and transferred securities	(9,069)	(22,828)	19,038
Derivative instruments:
Net unrealized gains (losses) on derivative instruments	825	(3,136)	(12,506)
Reclassification adjustment for net loss included in net income	5,087	5,686	5,182
Total derivative instruments	5,912	2,550	(7,324)
Defined benefit pension and other postretirement benefit plans:
Current year actuarial loss	(232)	(5,500)	(21,329)
Reclassification adjustment for amortization of net loss included in net income	4,493	3,887	1,856
Reclassification adjustment for prior service cost included in net income	9	46	47
Total defined benefit pension and postretirement benefit plans	4,270	(1,567)	(19,426)
Other Comprehensive Income (Loss), Pre-Tax Amount	1,745	(34,628)	(12,114)
Other Comprehensive Income (Loss), Tax Benefit (Expense)	(632)	12,783	4,402
Other comprehensive income (loss), net of tax	$ 1,113	$ (21,845)	$ (7,712)