Investment Securities - Held-to-Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2023		Dec. 31, 2022	Dec. 31, 2021
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	$ 2,288,791		$ 2,270,635
(fair value of $2,168,316 and $2,110,472, respectively)	2,287,291	[1]	2,269,135
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	1,760	[1]	8
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(120,735)	[1]	(158,671)
Debt Securities, Held-to-maturity, Fair Value	2,168,316	[1]	2,110,472
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	(1,500)	[1]	(1,500)	$ 0
US States and Political Subdivisions Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	1,247,310		1,243,443
(fair value of $2,168,316 and $2,110,472, respectively)	1,247,170		1,243,303
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	1,760		8
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(28,170)		(77,526)
Debt Securities, Held-to-maturity, Fair Value	1,220,760		1,165,785
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	(140)		(140)
Commercial Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	433,827		427,411
(fair value of $2,168,316 and $2,110,472, respectively)	433,827		427,411
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0		0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(30,665)		(34,287)
Debt Securities, Held-to-maturity, Fair Value	403,162		393,124
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	0		0
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	350,493		345,825
(fair value of $2,168,316 and $2,110,472, respectively)	350,493		345,825
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0		0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(29,289)		(26,027)
Debt Securities, Held-to-maturity, Fair Value	321,204		319,798
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	0		0
US Treasury Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	187,033		184,162
(fair value of $2,168,316 and $2,110,472, respectively)	187,033		184,162
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0		0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(11,454)		(12,462)
Debt Securities, Held-to-maturity, Fair Value	175,579
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	0		0
Corporate Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	70,128		69,794
Interest Receivable	13,400		13,500
(fair value of $2,168,316 and $2,110,472, respectively)	68,768		68,434
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0		0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(21,157)		(8,369)
Debt Securities, Held-to-maturity, Fair Value	47,611		60,065
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	$ (1,360)		$ (1,360)

[1] Excludes accrued interest receivable of $13.4 million at December 31, 2023 which is recorded in "Other assets" on the consolidated balance shee