Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 80,069	$ (54,724)
Net change in unrealized gain or loss	(145,490)	165,297
Reclassification of net income or loss realized and included in earnings	286	368
Amortization of unrealized net loss (gain) on securities transferred to HTM	(56)	(195)
Income tax expense (benefit)	(33,748)	37,480
Ending Balance	(31,443)	73,266
Equity Method Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5,369)	(434)
Net change in unrealized gain or loss	462	(197)
Reclassification of net income or loss realized and included in earnings	4,468
Ending Balance	(439)	(631)
Accumulated Other Comprehensive Loss Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	171,224	28,950
Net change in unrealized gain or loss	(141,800)	124,018
Income tax expense (benefit)	(31,862)	28,056
Ending Balance	61,286	124,912
Held to Maturity Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	276	639
Amortization of unrealized net loss (gain) on securities transferred to HTM	(56)	(195)
Income tax expense (benefit)	(13)	(44)
Ending Balance	233	488
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(125,573)	(101,278)
Reclassification of net income or loss realized and included in earnings	1,954	1,232
Income tax expense (benefit)	439	279
Ending Balance	(124,058)	(100,325)
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	39,511	17,399
Net change in unrealized gain or loss	(4,152)	41,476
Reclassification of net income or loss realized and included in earnings	(6,136)	(864)
Income tax expense (benefit)	(2,312)	9,189
Ending Balance	$ 31,535	$ 48,822