Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost
Available for Sale, Due in one year or less	$ 7,436
Available for Sale, Due after one year through five years	190,843
Available for Sale, Due after five years through ten years	136,473
Available for Sale, Due after ten years	34,611
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	369,363
Available for Sale, Total debt securities	3,816,198	$ 2,997,032
Fair Value
Available for Sale, Due in one year or less	7,368
Available for Sale, Due after one year through five years	170,918
Available for Sale, Due after five years through ten years	125,923
Available for Sale, Due after ten years	31,636
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	335,846
Available for Sale, Total debt securities	$ 3,491,679	2,742,025
Available for Sale, Ratio of Fair Value to Amortized Cost	91.50%
Amortized Cost
Held to Maturity, Due in one year or less	$ 16,715
Held to Maturity, Due after one year through five years	47,774
Held to Maturity, Due after five years through ten years	155,329
Held to Maturity, Due after ten years	1,481,344
Held to Maturity, Total Debt Securities	1,701,161
Held to Maturity, Amortized Cost	3,900,483	3,960,451
Fair Value
Held to Maturity, Due in one year or less	16,673
Held to Maturity, Due after one year through five years	46,115
Held to Maturity, Due after five years through ten years	144,145
Held to Maturity, Due after ten years	1,214,531
Held to Maturity, Securities, Debt Securities	1,421,464
Held to Maturity, Total debt securities at fair value	$ 3,145,898	3,401,018
Held to Maturity, Ratio of Fair Value to Amortized Cost	80.70%
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Amortized Cost
Available for Sale, Total debt securities	$ 0
Fair Value
Available for Sale, Total debt securities	0
Amortized Cost
Held to Maturity, Amortized Cost	349,410	364,728
Fair Value
Held to Maturity, Total debt securities at fair value	274,518	303,505
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Amortized Cost
Available for Sale, Total debt securities	140,881	157,138
Fair Value
Available for Sale, Total debt securities	138,514	151,191
Amortized Cost
Held to Maturity, Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities at fair value	0
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost
Available for Sale, Total debt securities	3,299	4,512
Fair Value
Available for Sale, Total debt securities	3,261	4,477
Amortized Cost
Held to Maturity, Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities at fair value	0
FNMA/FHLMC \| Residential Related Securities
Amortized Cost
Available for Sale, Total debt securities	1,678,641	1,820,642
Fair Value
Available for Sale, Total debt securities	1,436,759	1,604,610
Amortized Cost
Held to Maturity, Amortized Cost	956,107	961,231
Fair Value
Held to Maturity, Total debt securities at fair value	763,567	816,771
FNMA/FHLMC \| Commercial mortgage-related securities
Amortized Cost
Available for Sale, Total debt securities	18,779	19,038
Fair Value
Available for Sale, Total debt securities	16,154	17,142
Amortized Cost
Held to Maturity, Amortized Cost	782,291	778,796
Fair Value
Held to Maturity, Total debt securities at fair value	589,097	615,839
Government National Mortgage Association (GNMA) [Member] \| Residential Related Securities
Amortized Cost
Available for Sale, Total debt securities	1,416,569	502,537
Fair Value
Available for Sale, Total debt securities	1,384,670	497,596
Amortized Cost
Held to Maturity, Amortized Cost	50,489	52,979
Fair Value
Held to Maturity, Total debt securities at fair value	45,312	49,628
Government National Mortgage Association (GNMA) [Member] \| Commercial mortgage-related securities
Amortized Cost
Available for Sale, Total debt securities	188,667	115,031
Fair Value
Available for Sale, Total debt securities	176,474	110,462
Amortized Cost
Held to Maturity, Amortized Cost	61,025	69,369
Fair Value
Held to Maturity, Total debt securities at fair value	$ 51,940	$ 62,691

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