Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 3,816,198	$ 2,997,032
Debt Securities, Available-for-sale, Unrealized Gain	207	830
Debt Securities, Available-for-sale, Unrealized Loss	(324,727)	(255,837)
AFS investment securities, at fair value	3,491,679	2,742,025
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	3,900,483	3,960,451
Held-to-maturity, Gross Unrealized Gains	52,043	60,978
Held-to-maturity, Gross Unrealized Loss	(806,627)	(620,411)
Held-to-maturity, Fair Value	3,145,898	3,401,018
US Treasury Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	124,555	124,441
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(15,531)	(15,063)
AFS investment securities, at fair value	109,024	109,378
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	999	999
Held-to-maturity, Gross Unrealized Gains	0	0
Held-to-maturity, Gross Unrealized Loss	(51)	(62)
Held-to-maturity, Fair Value	948	936
Agency Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	15,000	15,000
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(1,410)	(1,468)
AFS investment securities, at fair value	13,590	13,532
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	226,808	235,693
Debt Securities, Available-for-sale, Unrealized Gain	0	96
Debt Securities, Available-for-sale, Unrealized Loss	(16,492)	(5,074)
AFS investment securities, at fair value	210,317	230,714
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	1,700,162	1,732,351
Held-to-maturity, Gross Unrealized Gains	12	1,994
Held-to-maturity, Gross Unrealized Loss	(279,659)	(182,697)
Held-to-maturity, Fair Value	1,420,516	1,551,647
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	0
AFS investment securities, at fair value	0
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	349,410	364,728
Held-to-maturity, Gross Unrealized Gains	10,228	11,697
Held-to-maturity, Gross Unrealized Loss	(85,120)	(72,920)
Held-to-maturity, Fair Value	274,518	303,505
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	140,881	157,138
Debt Securities, Available-for-sale, Unrealized Gain	83	0
Debt Securities, Available-for-sale, Unrealized Loss	(2,450)	(5,947)
AFS investment securities, at fair value	138,514	151,191
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	0
Held-to-maturity, Fair Value	0
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,299	4,512
Debt Securities, Available-for-sale, Unrealized Gain	9	15
Debt Securities, Available-for-sale, Unrealized Loss	(46)	(51)
AFS investment securities, at fair value	3,261	4,477
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	0
Held-to-maturity, Fair Value	0
Other Debt securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,000	3,000
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(85)	(78)
AFS investment securities, at fair value	2,915	2,922
FNMA/FHLMC | Residential Related Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,678,641	1,820,642
Debt Securities, Available-for-sale, Unrealized Gain	115	404
Debt Securities, Available-for-sale, Unrealized Loss	(241,997)	(216,436)
AFS investment securities, at fair value	1,436,759	1,604,610
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	956,107	961,231
Held-to-maturity, Gross Unrealized Gains	28,038	31,301
Held-to-maturity, Gross Unrealized Loss	(220,577)	(175,760)
Held-to-maturity, Fair Value	763,567	816,771
FNMA/FHLMC | Commercial mortgage-related securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	18,779	19,038
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(2,625)	(1,896)
AFS investment securities, at fair value	16,154	17,142
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	782,291	778,796
Held-to-maturity, Gross Unrealized Gains	13,329	15,324
Held-to-maturity, Gross Unrealized Loss	(206,522)	(178,281)
Held-to-maturity, Fair Value	589,097	615,839
Government National Mortgage Association (GNMA) [Member] | Residential Related Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,416,569	502,537
Debt Securities, Available-for-sale, Unrealized Gain	0	314
Debt Securities, Available-for-sale, Unrealized Loss	(31,898)	(5,255)
AFS investment securities, at fair value	1,384,670	497,596
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	50,489	52,979
Held-to-maturity, Gross Unrealized Gains	15	85
Held-to-maturity, Gross Unrealized Loss	(5,192)	(3,436)
Held-to-maturity, Fair Value	45,312	49,628
Government National Mortgage Association (GNMA) [Member] | Commercial mortgage-related securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	188,667	115,031
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(12,193)	(4,569)
AFS investment securities, at fair value	176,474	110,462
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	61,025	69,369
Held-to-maturity, Gross Unrealized Gains	421	577
Held-to-maturity, Gross Unrealized Loss	(9,506)	(7,254)
Held-to-maturity, Fair Value	$ 51,940	$ 62,691