Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized Cost
Available for Sale, Due in one year or less	$ 5,167
Available for Sale, Due after one year through five years	89,914
Available for Sale, Due after five years through ten years	378,692
Available for Sale, Due after ten years	37,386
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	505,706
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	511,159
Available for Sale, Total debt securities	2,890,763	$ 4,338,671
Available for Sale, amortized cost	2,890,763	4,338,671
Fair Value
Available for Sale, Due in one year or less	5,171
Available for Sale, Due after one year through five years	87,185
Available for Sale, Due after five years through ten years	374,733
Available for Sale, Due after ten years	$ 38,617
Available for Sale, Total debt securities		4,332,015
Available for Sale, Ratio of Fair Value to Amortized Cost	96.20%
Investment securities AFS, at fair value	$ 2,780,803	4,332,015
Amortized Cost
Held to Maturity, Due in one year or less	18,432
Held to Maturity, Due after one year through five years	34,156
Held to Maturity, Due after five years through ten years	163,456
Held to Maturity, Due after ten years	1,481,489
Held to Maturity, Total Debt Securities	1,697,534
Held to Maturity, Amortized Cost	3,939,920	2,239,003
Fair Value
Held to Maturity, Due in one year or less	18,503
Held to Maturity, Due after one year through five years	34,343
Held to Maturity, Due after five years through ten years	164,057
Held to Maturity, Due after ten years	1,431,903
Held to Maturity, Securities, Debt Securities	1,648,806
Held to Maturity, Total debt securities at fair value	$ 3,764,901	2,348,664
Held to Maturity, Ratio of Fair Value to Amortized Cost	95.60%
Residential Related Securities \| FNMA/FHLMC
Amortized Cost
Available for Sale, Total debt securities	$ 1,993,893	2,709,399
Available for Sale, amortized cost	1,993,893	2,709,399
Fair Value
Available for Sale, Total debt securities	1,894,819
Amortized Cost
Held to Maturity, Amortized Cost	956,470	34,347
Fair Value
Held to Maturity, Total debt securities at fair value	919,790	36,139
Residential Related Securities \| Government National Mortgage Association (GNMA) [Member]
Amortized Cost
Available for Sale, Total debt securities	59,470	66,189
Available for Sale, amortized cost	59,470	66,189
Fair Value
Available for Sale, Total debt securities	58,909
Amortized Cost
Held to Maturity, Amortized Cost	44,742	48,053
Fair Value
Held to Maturity, Total debt securities at fair value	44,215	49,631
Commercial mortgage-related securities \| FNMA/FHLMC
Amortized Cost
Available for Sale, Total debt securities	19,290	357,240
Available for Sale, amortized cost	19,290	357,240
Fair Value
Available for Sale, Total debt securities	19,786
Amortized Cost
Held to Maturity, Amortized Cost	764,775	425,937
Fair Value
Held to Maturity, Total debt securities at fair value	693,610	419,400
Commercial mortgage-related securities \| Government National Mortgage Association (GNMA) [Member]
Amortized Cost
Available for Sale, Total debt securities	128,019	165,439
Available for Sale, amortized cost	128,019	165,439
Fair Value
Available for Sale, Total debt securities	126,760
Amortized Cost
Held to Maturity, Amortized Cost	92,383	100,907
Fair Value
Held to Maturity, Total debt securities at fair value	89,959	102,506
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Amortized Cost
Available for Sale, Total debt securities	173,068	177,974
Available for Sale, amortized cost	173,068	177,974
Fair Value
Available for Sale, Total debt securities	168,978
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	5,865	6,594
Available for Sale, amortized cost	5,865	6,594
Fair Value
Available for Sale, Total debt securities	5,845
Amortized Cost
Held to Maturity, Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities at fair value	0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Amortized Cost
Available for Sale, Total debt securities	0	332,028
Available for Sale, amortized cost	0	332,028
Fair Value
Available for Sale, Total debt securities	0	$ 329,724
Amortized Cost
Held to Maturity, Amortized Cost	384,016
Fair Value
Held to Maturity, Total debt securities at fair value	$ 368,521

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