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Investment Securities - Schedule of Amortized Cost and Fair Value by Contractual Maturity of Investment Securities HTM and AFS (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Investment securities HTM, Fair value
Fair value	$ 2,466,265	$ 2,524,525
Investment securities AFS, Amortized cost
Amortized Cost	7,862,915	8,079,918
Investment securities AFS, Fair value
Fair value	7,575,468	7,551,018
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Investment securities HTM, Amortized cost
Within One Year	0
1 to 5 Years	0
5 to 10 Years	0
More Than 10 Years	2,450,885
Amortized cost	2,450,885
Investment securities HTM, Fair value
Within One Year	0
1 to 5 Years	0
5 to 10 Years	0
More Than 10 Years	2,466,265
Fair value	2,466,265	2,524,525
Investment securities AFS, Amortized cost
Within One Year	0
1 to 5 Years	0
5 to 10 Years	0
More Than 10 Years	2,177,658
Amortized Cost	2,177,658	2,294,700
Investment securities AFS, Fair value
Within One Year	0
1 to 5 Years	0
5 to 10 Years	0
More Than 10 Years	2,006,151
Fair value	2,006,151	2,034,035
U.S. Treasury securities
Investment securities AFS, Amortized cost
Within One Year	211,755
1 to 5 Years	909,695
5 to 10 Years	78,863
More Than 10 Years	0
Amortized Cost	1,200,313	1,214,363
Investment securities AFS, Fair value
Within One Year	212,743
1 to 5 Years	927,008
5 to 10 Years	81,403
More Than 10 Years	0
Fair value	1,221,154	1,212,742
U.S. Government agency securities
Investment securities AFS, Amortized cost
Within One Year	0
1 to 5 Years	29,995
5 to 10 Years	0
More Than 10 Years	0
Amortized Cost	29,995	29,993
Investment securities AFS, Fair value
Within One Year	0
1 to 5 Years	29,857
5 to 10 Years	0
More Than 10 Years	0
Fair value	29,857	29,163
Mortgage-backed securities issued by U.S. Government agencies
Investment securities AFS, Amortized cost
Within One Year	0
1 to 5 Years	29
5 to 10 Years	2
More Than 10 Years	1,504,863
Amortized Cost	1,504,894	1,583,331
Investment securities AFS, Fair value
Within One Year	0
1 to 5 Years	28
5 to 10 Years	2
More Than 10 Years	1,429,676
Fair value	1,429,706	1,462,790
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Investment securities AFS, Amortized cost
Within One Year	0
1 to 5 Years	7
5 to 10 Years	7,324
More Than 10 Years	596,196
Amortized Cost	603,527	657,453
Investment securities AFS, Fair value
Within One Year	0
1 to 5 Years	7
5 to 10 Years	7,225
More Than 10 Years	511,967
Fair value	519,199	550,201
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Investment securities AFS, Amortized cost
Within One Year	54,439
1 to 5 Years	1,495,206
5 to 10 Years	770,975
More Than 10 Years	16,723
Amortized Cost	2,337,343	2,290,968
Investment securities AFS, Fair value
Within One Year	53,261
1 to 5 Years	1,509,841
5 to 10 Years	782,568
More Than 10 Years	14,540
Fair value	2,360,210	2,253,116
Corporate debt securities and other debt securities
Investment securities AFS, Amortized cost
Within One Year	0
1 to 5 Years	9,185
5 to 10 Years	0
More Than 10 Years	0
Amortized Cost	9,185	9,110
Investment securities AFS, Fair value
Within One Year	0
1 to 5 Years	9,191
5 to 10 Years	0
More Than 10 Years	0
Fair value	$ 9,191	$ 8,971

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