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Available for Sale Securities (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2024
USD ($)
Mar. 31, 2023
USD ($)
Dec. 31, 2023
USD ($)
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost $ 13,296,347   $ 12,903,305
Available-for-sale Securities, Fair Value 12,653,088   12,286,681
Available-for-sale Securities, Gross Unrealized Gain 32,435   52,821
Available-for-sale Securities, Gross Unrealized Loss (675,694)   $ (669,445)
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Available-for-sale Securities, Proceeds 735,994 $ 0  
Available-for-sale Securities, Gross realized gains 233 0  
Available-for-sale Securities, Gross realized losses (45,404) 0  
Available-for-sale Securities, Related federal and state income tax expense (benefit) $ (10,624) $ 0  
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 1,131   1,123
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 2,562,022   $ 1,205,822
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 13,686   7,969
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 7,483,659   8,087,455
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 662,008   661,476
Debt Securities, Available-for-sale, Unrealized Loss Position 10,045,681   9,293,277
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss 675,694   669,445
Asset Pledged as Collateral with Right      
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Pledged Securities 18,900,000   13,900,000
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 473,589    
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis 2,480,160    
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis 915,033    
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis 447,154    
Available-for-sale Securities, Debt Maturities, Allocated and Single Maturity Date, Amortized Cost 4,315,936    
Debt Securities, Available-for-sale, Maturity, Fair Value, Rolling Maturity [Abstract]      
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value 468,688    
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value 2,254,408    
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value 841,253    
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value 425,246    
Available-for-sale Securities, Debt Maturities, Allocated and Single Maturity Date, Fair Value $ 3,989,595    
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity [1] 5.19    
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 920   925
Available-for-sale Securities, Gross Unrealized Gain 0   0
Available-for-sale Securities, Gross Unrealized Loss $ (80)   $ (75)
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 1   1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 0   $ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0   0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 920   925
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 80   75
Debt Securities, Available-for-sale, Unrealized Loss Position 920   925
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss 80   75
Municipal securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost 329,216   544,707
Available-for-sale Securities, Fair Value 304,826   502,833
Available-for-sale Securities, Gross Unrealized Gain 0   1
Available-for-sale Securities, Gross Unrealized Loss $ (24,390)   $ (41,875)
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 135   190
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 3,139   $ 6,799
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 30   410
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 298,162   494,955
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 24,360   41,465
Debt Securities, Available-for-sale, Unrealized Loss Position 301,301   501,754
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss 24,390   41,875
Commercial agency mortgage-backed securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost 3,985,220   4,456,918
Available-for-sale Securities, Fair Value 3,683,376   4,147,853
Available-for-sale Securities, Gross Unrealized Gain 1,197   2,972
Available-for-sale Securities, Gross Unrealized Loss $ (303,041)   $ (312,037)
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 245   269
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 241,331   $ 392,828
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 2,625   2,626
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 3,148,535   3,421,757
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 300,416   309,411
Debt Securities, Available-for-sale, Unrealized Loss Position 3,389,866   3,814,585
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss 303,041   312,037
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)
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 1   1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 0   $ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0   0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 473   473
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 27   27
Debt Securities, Available-for-sale, Unrealized Loss Position 473   473
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated 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] 8,980,411    
Debt Securities, Available-for-sale, Maturity, Fair Value, Rolling Maturity [Abstract]      
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value $ 8,663,493    
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 $ 8,095,352   7,066,645
Available-for-sale Securities, Fair Value 7,816,688   6,834,720
Available-for-sale Securities, Gross Unrealized Gain 20,132   36,983
Available-for-sale Securities, Gross Unrealized Loss $ (298,796)   $ (268,908)
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 711   630
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 2,179,355   $ 690,118
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 10,501   3,689
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 3,502,950   3,717,975
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 288,296   265,219
Debt Securities, Available-for-sale, Unrealized Loss Position 5,682,306   4,408,093
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss 298,797   268,908
Residential non-agency mortgage-backed securities [Member]      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale Securities, Amortized Cost 885,059   833,535
Available-for-sale Securities, Fair Value 846,805   799,877
Available-for-sale Securities, Gross Unrealized Gain 11,106   12,865
Available-for-sale Securities, Gross Unrealized Loss $ (49,360)   $ (46,523)
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]      
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 38   32
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value $ 138,197   $ 116,077
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 530   1,244
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 532,619   451,370
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 48,829   45,279
Debt Securities, Available-for-sale, Unrealized Loss Position 670,815   567,447
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss $ 49,359   $ 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 4.2 years based upon current prepayment assumptions.