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Available for Sale Securities (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2025
USD ($)
Mar. 31, 2024
USD ($)
Dec. 31, 2024
USD ($)
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost $ 13,466,384   $ 13,388,935
Available-for-sale Securities, Fair Value 13,102,877   12,851,600
Available-for-sale Securities, Gross Unrealized Gain 72,031   29,911
Available-for-sale Securities, Gross Unrealized Loss (435,538)   (567,246)
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Available-for-sale Securities, Proceeds 0 $ 735,994  
Available-for-sale Securities, Gross realized gains 0 233  
Available-for-sale Securities, Gross realized losses 0 (45,404)  
Available-for-sale Securities, Related federal and state income tax expense (benefit) 0 $ (10,624)  
Asset Pledged as Collateral with Right      
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Pledged Securities 11,400,000   9,900,000
Fixed Maturity Securities [Member]      
Debt Securities, Available-for-sale, Maturity, Amortized Cost, Rolling Maturity [Abstract]      
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis 275,064    
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis 2,520,815    
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis 493,021    
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis 418,056    
Available-for-sale Securities, Debt Maturities, Allocated and Single Maturity Date, Amortized Cost 3,706,956    
Debt Securities, Available-for-sale, Maturity, Fair Value, Rolling Maturity [Abstract]      
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value 272,659    
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value 2,366,001    
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value 458,539    
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value 406,212    
Available-for-sale Securities, Debt Maturities, Allocated and Single Maturity Date, Fair Value $ 3,503,411    
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity [1] 4.84    
U.S. Treasury [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost $ 1,000   1,000
Available-for-sale Securities, Fair Value 957   945
Available-for-sale Securities, Gross Unrealized Gain 0   0
Available-for-sale Securities, Gross Unrealized Loss (43)   (55)
Municipal securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost 234,552   240,528
Available-for-sale Securities, Fair Value 222,282   225,568
Available-for-sale Securities, Gross Unrealized Gain 1   2
Available-for-sale Securities, Gross Unrealized Loss (12,271)   (14,962)
Commercial agency mortgage-backed securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost 3,470,904   3,436,465
Available-for-sale Securities, Fair Value 3,279,699   3,204,016
Available-for-sale Securities, Gross Unrealized Gain 3,326   726
Available-for-sale Securities, Gross Unrealized Loss (194,531)   (233,175)
Other debt securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost 500   500
Available-for-sale Securities, Fair Value 473   473
Available-for-sale Securities, Gross Unrealized Gain 0   0
Available-for-sale Securities, Gross Unrealized Loss (27)   (27)
Residential Mortgage Backed Securities [Member]      
Debt Securities, Available-for-sale, Maturity, Amortized Cost, Rolling Maturity [Abstract]      
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost [2] 9,759,428    
Debt Securities, Available-for-sale, Maturity, Fair Value, Rolling Maturity [Abstract]      
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value $ 9,599,466    
Available-for-sale Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities 4 years 2 months 12 days    
Residential agency mortgage-backed securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost $ 8,974,553   8,895,900
Available-for-sale Securities, Fair Value 8,839,322   8,639,389
Available-for-sale Securities, Gross Unrealized Gain 56,854   17,936
Available-for-sale Securities, Gross Unrealized Loss (192,085)   (274,447)
Residential non-agency mortgage-backed securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost 784,875   814,542
Available-for-sale Securities, Fair Value 760,144   781,209
Available-for-sale Securities, Gross Unrealized Gain 11,850   11,247
Available-for-sale Securities, Gross Unrealized Loss $ (36,581)   $ (44,580)
[1] Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.
[2] The average expected lives of residential mortgage-backed securities were 4.2 years based upon current prepayment assumptions.