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Available for Sale Securities (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Available for Sale Securities [Line Items]      
Available for sale securities, Amortized Cost $ 13,388,935 $ 12,903,305  
Available for sale securities 12,851,600 12,286,681  
Available for sale securities, Gross Unrealized Gain 29,911 52,821  
Available for sale securities, Gross Unrealized Loss (567,246) (669,445)  
Available for Sale Securities, Realized Gain (Loss) [Abstract]      
Proceeds from sales of available for sale securities 839,352 834,704 $ 307,481
Available for sale securities, Gross realized gains 2,257 1,180 5,054
Available for sale securities, Gross realized losses (48,085) (31,816) (6,025)
Available for sale securities, Related federal and state income tax expense (10,779) (7,206) $ (227)
Asset Pledged as Collateral with Right      
Available for Sale Securities, Realized Gain (Loss) [Abstract]      
Pledged Securities 9,900,000 13,900,000  
Fixed maturity securities [Member]      
Available for Sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]      
Available for sale securities, Debt Maturities, Less than One Year, Amortized Cost 236,710    
Available for sale securities, Debt Maturities, One to Five Years, Amortized Cost 2,469,580    
Available for sale securities, Debt Maturities, Six to Ten Years, Amortized Cost 544,215    
Available for sale securities, Debt Maturities, Over Ten Years, Amortized Cost 427,988    
Available for sale securities, Maturity, Allocated and Single Maturity Date, Amortized Cost 3,678,493    
Available for Sale Securities, Maturity, Fair Value, Rolling Maturity [Abstract]      
Available for sale securities, Debt Maturities, Less Than One Year, Fair Value 234,816    
Available for sale securities, Debt Maturities, One to Five Years, Fair Value 2,290,038    
Available for sale securities, Debt Maturities, Six to Ten Years, Fair Value 493,883    
Available for sale securities, Debt Maturities, Over Ten Years, Fair Value 412,265    
Available for sale securities, Debt Maturities, Single Maturity Date, Fair value $ 3,431,002    
Available for sale securities, Debt Maturities, Weighted Average Maturity [1] 4.99    
U.S. Treasury [Member]      
Available for Sale Securities [Line Items]      
Available for sale securities, Amortized Cost $ 1,000 1,000  
Available for sale securities 945 925  
Available for sale securities, Gross Unrealized Gain 0 0  
Available for sale securities, Gross Unrealized Loss (55) (75)  
Municipal securities [Member]      
Available for Sale Securities [Line Items]      
Available for sale securities, Amortized Cost 240,528 544,707  
Available for sale securities 225,568 502,833  
Available for sale securities, Gross Unrealized Gain 2 1  
Available for sale securities, Gross Unrealized Loss (14,962) (41,875)  
Commercial agency mortgage-backed securities [Member]      
Available for Sale Securities [Line Items]      
Available for sale securities, Amortized Cost 3,436,465 4,456,918  
Available for sale securities 3,204,016 4,147,853  
Available for sale securities, Gross Unrealized Gain 726 2,972  
Available for sale securities, Gross Unrealized Loss (233,175) (312,037)  
Other debt securities [Member]      
Available for Sale Securities [Line Items]      
Available for sale securities, Amortized Cost 500 500  
Available for sale securities 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]      
Available for Sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]      
Available for sale securities, Maturity, without Single Maturity Date, Amortized Cost [2] 9,710,442    
Available for Sale Securities, Maturity, Fair Value, Rolling Maturity [Abstract]      
Available for sale securities, Debt Maturities, without Single Maturity Date, Fair value $ 9,420,598    
Available for sale securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities 4 years 4 months 24 days    
Residential agency mortgage-backed securities [Member]      
Available for Sale Securities [Line Items]      
Available for sale securities, Amortized Cost $ 8,895,900 7,066,645  
Available for sale securities 8,639,389 6,834,720  
Available for sale securities, Gross Unrealized Gain 17,936 36,983  
Available for sale securities, Gross Unrealized Loss (274,447) (268,908)  
Residential non-agency mortgage-backed securities [Member]      
Available for Sale Securities [Line Items]      
Available for sale securities, Amortized Cost 814,542 833,535  
Available for sale securities 781,209 799,877  
Available for sale securities, Gross Unrealized Gain 11,247 12,865  
Available for sale securities, Gross Unrealized Loss $ (44,580) $ (46,523)  
[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 4.4 years based upon current prepayment assumptions.