Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,575,036	$ 3,740,413
Gross Unrealized Gains	7,307	6,651
Gross Unrealized Losses	(377,847)	(444,752)
Fair Value	3,204,496	3,302,312
Allowance for Credit Losses	1,076	1,205	$ 1,321	$ 1,090	$ 1,646	$ 1,351
Net Carrying Value	3,573,960	3,739,208
U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	25,671	26,232
Gross Unrealized Gains	11	0
Gross Unrealized Losses	0	(254)
Fair Value	25,682	25,978
Allowance for Credit Losses	0	0
Net Carrying Value	25,671	26,232
U.S. government agency securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	303,200	305,996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(33,992)	(44,441)
Fair Value	269,208	261,555
Allowance for Credit Losses	0	0
Net Carrying Value	303,200	305,996
Obligations of states and state agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	75,529	88,556
Gross Unrealized Gains	273	552
Gross Unrealized Losses	(3,536)	(4,155)
Fair Value	72,266	84,953
Allowance for Credit Losses	389	395
Net Carrying Value	75,140	88,161
Municipal bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	305,124	316,914
Gross Unrealized Gains	42	40
Gross Unrealized Losses	(13,142)	(14,380)
Fair Value	292,024	302,574
Allowance for Credit Losses	45	49
Net Carrying Value	305,079	316,865
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	380,653	405,470
Gross Unrealized Gains	315	592
Gross Unrealized Losses	(16,678)	(18,535)
Fair Value	364,290	387,527
Allowance for Credit Losses	434	444
Net Carrying Value	380,219	405,026
Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,742,188	2,885,303
Gross Unrealized Gains	6,946	6,059
Gross Unrealized Losses	(316,267)	(369,436)
Fair Value	2,432,867	2,521,926
Allowance for Credit Losses	0	0
Net Carrying Value	2,742,188	2,885,303
Trust preferred securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	37,076	37,062
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7,302)	(6,412)
Fair Value	29,774	30,650
Allowance for Credit Losses	440	506
Net Carrying Value	36,636	36,556
Corporate and other debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	86,248	80,350
Gross Unrealized Gains	35	0
Gross Unrealized Losses	(3,608)	(5,674)
Fair Value	82,675	74,676
Allowance for Credit Losses	202	255
Net Carrying Value	$ 86,046	$ 80,095