Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Amortized Cost
Available for Sale, Due in one year or less	$ 6,905
Available for Sale, Due after one year through five years	98,473
Available for Sale, Due after five years through ten years	361,344
Available for Sale, Due after ten years	37,355
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	504,077
Available for Sale, Total debt securities	2,852,501	$ 4,338,671
Fair Value
Available for Sale, Due in one year or less	6,895
Available for Sale, Due after one year through five years	94,572
Available for Sale, Due after five years through ten years	350,609
Available for Sale, Due after ten years	36,762
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	488,839
Available for Sale, Total debt securities	$ 2,677,511	4,332,015
Available for Sale, Ratio of Fair Value to Amortized Cost	93.90%
Amortized Cost
Held to Maturity, Due in one year or less	$ 15,582
Held to Maturity, Due after one year through five years	34,915
Held to Maturity, Due after five years through ten years	169,413
Held to Maturity, Due after ten years	1,498,715
Held to Maturity, Total Debt Securities	1,718,625
Held to Maturity, Amortized Cost	3,945,269	2,239,003
Fair Value
Held to Maturity, Due in one year or less	15,627
Held to Maturity, Due after one year through five years	35,027
Held to Maturity, Due after five years through ten years	167,713
Held to Maturity, Due after ten years	1,343,101
Held to Maturity, Securities, Debt Securities	1,561,468
Held to Maturity, Total debt securities at fair value	$ 3,534,192	2,348,664
Held to Maturity, Ratio of Fair Value to Amortized Cost	89.60%
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Amortized Cost
Available for Sale, Total debt securities	$ 0	332,028
Fair Value
Available for Sale, Total debt securities	0	329,724
Amortized Cost
Held to Maturity, Amortized Cost	375,638
Fair Value
Held to Maturity, Total debt securities at fair value	333,841
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Amortized Cost
Available for Sale, Total debt securities	168,357	177,974
Fair Value
Available for Sale, Total debt securities	161,264	177,325
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	5,287	6,594
Fair Value
Available for Sale, Total debt securities	5,281	6,580
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	1,959,641	2,709,399
Fair Value
Available for Sale, Total debt securities	1,811,603	2,691,879
Amortized Cost
Held to Maturity, Amortized Cost	967,421	34,347
Fair Value
Held to Maturity, Total debt securities at fair value	876,085	36,139
FNMA/FHLMC \| Commercial mortgage-related securities
Amortized Cost
Available for Sale, Total debt securities	19,207	357,240
Fair Value
Available for Sale, Total debt securities	18,606	350,623
Amortized Cost
Held to Maturity, Amortized Cost	762,086	425,937
Fair Value
Held to Maturity, Total debt securities at fair value	647,070	419,400
Government National Mortgage Association (GNMA) [Member] \| Residential Related Securities
Amortized Cost
Available for Sale, Total debt securities	87,779	66,189
Fair Value
Available for Sale, Total debt securities	86,238	67,780
Amortized Cost
Held to Maturity, Amortized Cost	42,248	48,053
Fair Value
Held to Maturity, Total debt securities at fair value	40,649	49,631
Government National Mortgage Association (GNMA) [Member] \| Commercial mortgage-related securities
Amortized Cost
Available for Sale, Total debt securities	108,153	165,439
Fair Value
Available for Sale, Total debt securities	105,680	166,799
Amortized Cost
Held to Maturity, Amortized Cost	79,250	100,907
Fair Value
Held to Maturity, Total debt securities at fair value	$ 75,079	$ 102,506

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Ratio of Fair Value to Amortized Cost, AFS

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