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Investment Securities - Expected maturities for residential mortgage backed securities (Details) - USD ($)
$ in Thousands
Sep. 30, 2022
Dec. 31, 2021
AFS Amortized Cost [Abstract]    
Amortized Cost $ 1,873,872 $ 2,642,667
AFS Estimated Fair Value [Abstract]    
Allowance for credit losses (18) (620)
Estimated Fair Value 1,649,753 2,623,408
HTM Amortized Cost [Abstract]    
Allowance for credit losses (802) 0
Amortized Cost 1,114,084 0
HTM Estimated Fair Value [Abstract]    
Investment securities, held-to-maturity, estimated fair value 989,001 0
Debt Securities, Available-for-Sale and Held-to-Maturity [Abstract]    
Amortized Cost 2,987,956 2,642,667
Estimated Fair Value 2,638,754 2,623,408
U.S. treasury bonds    
AFS Amortized Cost [Abstract]    
One year or less 49,767 49,693
Amortized Cost 49,767 49,693
AFS Estimated Fair Value [Abstract]    
One year or less 46,048 49,458
Allowance for credit losses 0 0
U. S. agency securities    
AFS Amortized Cost [Abstract]    
One year or less 535,826 425,597
After one year through five years 160,848 141,537
After five years through ten years 54,323 62,092
Amortized Cost 750,997 629,273
AFS Estimated Fair Value [Abstract]    
One year or less 474,498 421,347
After one year through five years 147,596 140,785
After five years through ten years 46,234 60,255
Allowance for credit losses 0 0
Residential mortgage-backed securities    
AFS Amortized Cost [Abstract]    
Residential mortgage-backed securities: 958,800 1,692,820
Amortized Cost 958,800 1,692,773
AFS Estimated Fair Value [Abstract]    
Residential mortgage-backed securities: 828,367 1,677,673
Allowance for credit losses 0 0
HTM Amortized Cost [Abstract]    
One year or less 761,304 0
Allowance for credit losses 0  
HTM Estimated Fair Value [Abstract]    
One year or less 674,281 0
Investment securities, held-to-maturity, estimated fair value 674,281  
Commercial mortgage-backed securities    
AFS Amortized Cost [Abstract]    
Residential mortgage-backed securities: 100,278 0
Amortized Cost 100,278  
AFS Estimated Fair Value [Abstract]    
Residential mortgage-backed securities: 94,172 0
Allowance for credit losses 0  
HTM Amortized Cost [Abstract]    
One year or less 92,948 0
Allowance for credit losses 0  
HTM Estimated Fair Value [Abstract]    
One year or less 81,733 0
Investment securities, held-to-maturity, estimated fair value 81,733  
Municipal bonds    
AFS Amortized Cost [Abstract]    
One year or less 1,600 4,806
After one year through five years 1,430 25,457
After five years through ten years 9,000 97,945
After ten years 0 13,708
Amortized Cost 12,030 141,916
AFS Estimated Fair Value [Abstract]    
One year or less 1,600 4,861
After one year through five years 1,441 26,816
After five years through ten years 7,953 99,960
After ten years 0 13,797
Allowance for credit losses (1) (3)
HTM Amortized Cost [Abstract]    
One year or less 3,161 0
After one year through five years 35,637 0
After five years through ten years 77,278 0
After ten years 12,310 0
Allowance for credit losses (16)  
HTM Estimated Fair Value [Abstract]    
One year or less 3,100 0
After one year through five years 32,630 0
After five years through ten years 66,457 0
After ten years 10,687 0
Investment securities, held-to-maturity, estimated fair value 112,874  
Corporate bonds    
AFS Amortized Cost [Abstract]    
One year or less 0 18,924
After one year through five years 2,000 54,630
After five years through ten years 0 55,458
Amortized Cost 2,000 129,012
AFS Estimated Fair Value [Abstract]    
One year or less 0 18,991
After one year through five years 1,862 54,833
After five years through ten years 0 55,252
Allowance for credit losses (17) (617)
HTM Amortized Cost [Abstract]    
One year or less 19,553 0
After one year through five years 89,358 0
After five years through ten years 23,337 0
Allowance for credit losses (786)  
HTM Estimated Fair Value [Abstract]    
One year or less 17,364 0
After one year through five years 82,204 0
After five years through ten years 20,545 $ 0
Investment securities, held-to-maturity, estimated fair value $ 120,113