Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net Income	$ 284,280	$ 286,981	$ 275,497
Unrealized gains (losses) on AFS investment securities:
Net unrealized holding gains (losses) 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 securities transferred to HTM	5,913	(44,483)	2,690
Net unrealized gains (losses) on AFS investment securities	41,369	(356,672)	(41,163)
Net unrealized holding losses arising during the period	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)
Net unrealized gains (losses) on interest rate derivatives used in cash flow hedges	26,993	(56,959)	(4,817)
Defined benefit pension plan and postretirement benefits:
Unrecognized pension and postretirement income (cost)	4,777	644	7,144
Amortization of net unrecognized pension and postretirement income (loss)	57	100	1,156
Net unrealized (losses) gains on defined benefit pension and postretirement plans	4,834	744	8,300
Other Comprehensive Income (Loss)	73,196	(412,887)	(37,680)
Total Comprehensive Income (Loss)	$ 357,476	$ (125,906)	$ 237,817