Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,651,454	$ 3,740,413
Gross Unrealized Gains	2,011	6,651
Gross Unrealized Losses	(513,517)	(444,752)
Fair Value	3,139,948	3,302,312
Allowance for Credit Losses	1,090	1,205	$ 1,351	$ 1,131	$ 1,646	$ 1,633
Net Carrying Value	3,650,364	3,739,208
U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	25,861	26,232
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(282)	(254)
Fair Value	25,579	25,978
Allowance for Credit Losses	0	0
Net Carrying Value	25,861	26,232
U.S. government agency securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	304,308	305,996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(46,851)	(44,441)
Fair Value	257,457	261,555
Allowance for Credit Losses	0	0
Net Carrying Value	304,308	305,996
Obligations of states and state agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	84,910	88,556
Gross Unrealized Gains	0	552
Gross Unrealized Losses	(5,303)	(4,155)
Fair Value	79,607	84,953
Allowance for Credit Losses	382	395
Net Carrying Value	84,528	88,161
Municipal bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	308,253	316,914
Gross Unrealized Gains	3	40
Gross Unrealized Losses	(21,252)	(14,380)
Fair Value	287,004	302,574
Allowance for Credit Losses	52	49
Net Carrying Value	308,201	316,865
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	393,163	405,470
Gross Unrealized Gains	3	592
Gross Unrealized Losses	(26,555)	(18,535)
Fair Value	366,611	387,527
Allowance for Credit Losses	434	444
Net Carrying Value	392,729	405,026
Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,804,769	2,885,303
Gross Unrealized Gains	2,008	6,059
Gross Unrealized Losses	(427,522)	(369,436)
Fair Value	2,379,255	2,521,926
Allowance for Credit Losses	0	0
Net Carrying Value	2,804,769	2,885,303
Trust preferred securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	37,071	37,062
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7,223)	(6,412)
Fair Value	29,848	30,650
Allowance for Credit Losses	445	506
Net Carrying Value	36,626	36,556
Corporate and other debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	86,282	80,350
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5,084)	(5,674)
Fair Value	81,198	74,676
Allowance for Credit Losses	211	255
Net Carrying Value	$ 86,071	$ 80,095