Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,711,818	$ 3,740,413
Gross Unrealized Gains	3,439	6,651
Gross Unrealized Losses	(497,855)	(444,752)
Fair Value	3,217,402	3,302,312
Allowance for Credit Losses	1,131	1,205	$ 1,633	$ 1,646
Net Carrying Value	3,710,687	3,739,208
U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	26,048	26,232
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(306)	(254)
Fair Value	25,742	25,978
Allowance for Credit Losses	0	0
Net Carrying Value	26,048	26,232
U.S. government agency securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	305,543	305,996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(45,368)	(44,441)
Fair Value	260,175	261,555
Allowance for Credit Losses	0	0
Net Carrying Value	305,543	305,996
Obligations of states and state agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	87,017	88,556
Gross Unrealized Gains	186	552
Gross Unrealized Losses	(4,632)	(4,155)
Fair Value	82,571	84,953
Allowance for Credit Losses	401	395
Net Carrying Value	86,616	88,161
Municipal bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	313,506	316,914
Gross Unrealized Gains	4	40
Gross Unrealized Losses	(18,049)	(14,380)
Fair Value	295,461	302,574
Allowance for Credit Losses	49	49
Net Carrying Value	313,457	316,865
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	400,523	405,470
Gross Unrealized Gains	190	592
Gross Unrealized Losses	(22,681)	(18,535)
Fair Value	378,032	387,527
Allowance for Credit Losses	450	444
Net Carrying Value	400,073	405,026
Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,856,322	2,885,303
Gross Unrealized Gains	3,249	6,059
Gross Unrealized Losses	(417,637)	(369,436)
Fair Value	2,441,934	2,521,926
Allowance for Credit Losses	0	0
Net Carrying Value	2,856,322	2,885,303
Trust preferred securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	37,066	37,062
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6,584)	(6,412)
Fair Value	30,482	30,650
Allowance for Credit Losses	454	506
Net Carrying Value	36,612	36,556
Corporate and other debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	86,316	80,350
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5,279)	(5,674)
Fair Value	81,037	74,676
Allowance for Credit Losses	227	255
Net Carrying Value	$ 86,089	$ 80,095