Investment Securities - Amortized Cost and Fair Value, by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 30,148
Due after one year through five years	39,854
Due after five years through ten years	178,200
Due after ten years	248,012
Total contractual maturities	496,214
Amortized Cost	8,733,170	$ 8,560,733
Fair Value
Due in one year or less	29,944
Due after one year through five years	38,512
Due after five years through ten years	172,750
Due after ten years	233,457
Total contractual maturities	474,663
Total available-for-sale securities, Fair value,	8,062,384	8,428,032
Mortgage-backed securities:
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	3,363,891
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	3,068,233
Residential - Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	128,080
Amortized Cost	128,080	135,764
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	122,965
Total available-for-sale securities, Fair value,	122,965	137,264
Residential - Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	1,450,070
Amortized Cost	1,450,070	1,496,605
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	1,362,345
Total available-for-sale securities, Fair value,	1,362,345	1,491,100
Commercial - Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	358,910
Amortized Cost	358,910	392,443
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	333,089
Total available-for-sale securities, Fair value,	333,089	387,663
Commercial - Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	1,426,831
Amortized Cost	1,426,831	1,415,511
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	1,249,834
Total available-for-sale securities, Fair value,	1,249,834	1,369,443
Collateralized mortgage obligations
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	4,873,065
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	4,519,488
Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	2,153,236
Amortized Cost	2,153,236	2,103,187
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	2,009,781
Total available-for-sale securities, Fair value,	2,009,781	2,079,523
Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	2,719,829
Amortized Cost	2,719,829	2,671,131
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	2,509,707
Total available-for-sale securities, Fair value,	$ 2,509,707	$ 2,621,044