Shareholders' Equity - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Before-Tax Amount
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax	$ 46,572	$ (403,606)	$ (23,222)
Reclassification adjustment for securities gains included in net income	(733)	(27)	(33,516)
Amortization of net unrealized losses on available for sale securities transferred to held to maturity	7,644	(57,509)	3,485
Net unrealized holding gains (loss) arising during the period on interest rate derivatives used in cash flow hedges	9,048	(81,400)	(3,452)
Reclassification adjustment for net loss (gain) realized in net income on interest rate derivatives used in cash flow hedges	25,850	7,761	(2,776)
Other comprehensive income, pension and other postretirement benefit plans, net unamortized gain (loss) arising during period, before tax	6,162	825	9,147
Amortization of net unrecognized pension and postretirement income	73	128	1,480
Other Comprehensive Income (Loss), before Tax, Total	94,616	(533,828)	(48,854)
Tax Effect
Unrealized gain (loss) on securities	(10,549)	91,437	5,274
Reclassification adjustment for securities gains included in net income	166	7	7,611
Amortization of net unrealized gains (losses) on AFS transferred to HTM	(1,731)	13,026	(795)
Net unrealized holding gains (loss) arising during the period on interest rate derivatives used in cash flow hedges	(2,050)	18,437	782
Reclassification adjustment for net loss (gain) realized in net income on interest rate derivatives used in cash flow hedges	(5,855)	(1,757)	629
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	(1,385)	(181)	(2,003)
Amortization of net unrecognized pension and postretirement income	(16)	(28)	(324)
Other Comprehensive Income (Loss), Tax	(21,420)	120,941	11,174
Other Comprehensive Income/(Loss), net of tax:
Unrealized gain (loss) on securities	36,023	(312,169)	(17,948)
Reclassification adjustment for securities gains (losses) included in net income	(567)	(20)	(25,905)
Amortization of net unrealized gains (losses) on AFS transferred to HTM	5,913	(44,483)	2,690
Net unrealized holding gains (loss) arising during the period on interest rate derivatives used in cash flow hedges	6,998	(62,963)	(2,670)
Reclassification adjustment for net loss (gain) realized in net income on interest rate derivatives used in cash flow hedges	19,995	6,004	(2,147)
Unrecognized pension and postretirement income (cost)	4,777	644	7,144
Amortization of net unrecognized pension and postretirement items	57	100	1,156
Total Other Comprehensive Income	$ 73,196	$ (412,887)	$ (37,680)