Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 3,902,762	$ 3,749,814
Debt Securities, Available-for-sale, Unrealized Gain	6,359	24,579
Debt Securities, Available-for-sale, Unrealized Loss	(184,973)	(173,501)
AFS investment securities, at fair value	3,724,148	3,600,892
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	3,833,043	3,860,235
Held-to-maturity, Gross Unrealized Gains	50,145	55,619
Held-to-maturity, Gross Unrealized Loss	(581,903)	(535,230)
Held-to-maturity, Fair Value	3,301,284	3,380,624
US Treasury Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	39,985	39,984
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(4,427)	(4,083)
AFS investment securities, at fair value	35,558	35,902
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	(30)	(36)
Held-to-maturity, Fair Value	969	963
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	83,823	94,008
Debt Securities, Available-for-sale, Unrealized Gain	1	23
Debt Securities, Available-for-sale, Unrealized Loss	(2,995)	(2,214)
AFS investment securities, at fair value	80,830	91,817
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	1,676,275	1,682,473
Held-to-maturity, Gross Unrealized Gains	2,292	5,638
Held-to-maturity, Gross Unrealized Loss	(154,833)	(134,053)
Held-to-maturity, Fair Value	1,523,734	1,554,059
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	341,153	345,083
Held-to-maturity, Gross Unrealized Gains	9,399	9,796
Held-to-maturity, Gross Unrealized Loss	(69,484)	(65,372)
Held-to-maturity, Fair Value	281,069	289,507
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	130,196	135,832
Debt Securities, Available-for-sale, Unrealized Gain	22	5
Debt Securities, Available-for-sale, Unrealized Loss	(1,065)	(1,862)
AFS investment securities, at fair value	129,154	133,975
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	916	1,077
Debt Securities, Available-for-sale, Unrealized Gain	1	2
Debt Securities, Available-for-sale, Unrealized Loss	(28)	(28)
AFS investment securities, at fair value	890	1,051
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	(35)	(50)
AFS investment securities, at fair value	2,965	2,950
US Government Sponsored-Enterprise Insured Loans | Residential Related Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,247,657	1,274,052
Debt Securities, Available-for-sale, Unrealized Gain	221	294
Debt Securities, Available-for-sale, Unrealized Loss	(156,880)	(153,552)
AFS investment securities, at fair value	1,090,998	1,120,794
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	930,148	941,973
Held-to-maturity, Gross Unrealized Gains	26,023	27,007
Held-to-maturity, Gross Unrealized Loss	(184,227)	(164,587)
Held-to-maturity, Fair Value	771,944	804,393
US Government Sponsored-Enterprise Insured Loans | Commercial mortgage-related securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	18,603	18,691
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(1,595)	(1,755)
AFS investment securities, at fair value	17,008	16,937
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	779,310	780,995
Held-to-maturity, Gross Unrealized Gains	12,068	12,699
Held-to-maturity, Gross Unrealized Loss	(162,450)	(160,781)
Held-to-maturity, Fair Value	628,928	632,914
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	2,219,058	2,021,242
Debt Securities, Available-for-sale, Unrealized Gain	6,114	24,254
Debt Securities, Available-for-sale, Unrealized Loss	(10,658)	(2,822)
AFS investment securities, at fair value	2,214,513	2,042,675
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	48,043	48,979
Held-to-maturity, Gross Unrealized Gains	24	92
Held-to-maturity, Gross Unrealized Loss	(3,609)	(2,901)
Held-to-maturity, Fair Value	44,457	46,170
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	159,523	161,928
Debt Securities, Available-for-sale, Unrealized Gain	0	0
Debt Securities, Available-for-sale, Unrealized Loss	(7,291)	(7,135)
AFS investment securities, at fair value	152,232	154,793
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	57,114	59,733
Held-to-maturity, Gross Unrealized Gains	338	386
Held-to-maturity, Gross Unrealized Loss	(7,270)	(7,500)
Held-to-maturity, Fair Value	$ 50,183	$ 52,619