Investment Securities Available for Sale - Amortized Cost And Estimated Fair Value By Contractual Maturity Of Investment Securities Available For Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized Cost
Amortized cost, within one year	$ 92,287
Amortized cost, 1 to 5 years	725,845
Amortized cost, 5 to 10 years	1,039,892
Amortized cost, more than 10 years	9,233,230
Amortized Cost	11,091,254	$ 11,273,327
Fair Value
Fair value, within one year	93,510
Fair value, 1 to 5 years	725,985
Fair value, 5 to 10 years	1,031,102
Fair value, more than 10 years	7,938,065
Total fair value	9,788,662	9,678,103
U.S. Treasury securities
Amortized Cost
Amortized cost, within one year	25,688
Amortized cost, 1 to 5 years	141,378
Amortized cost, 5 to 10 years	421,016
Amortized cost, more than 10 years	0
Amortized Cost	588,082	515,953
Fair Value
Fair value, within one year	25,688
Fair value, 1 to 5 years	143,641
Fair value, 5 to 10 years	428,300
Fair value, more than 10 years	0
Total fair value	597,629	471,813
U.S. Government agency securities
Amortized Cost
Amortized cost, within one year	0
Amortized cost, 1 to 5 years	29,993
Amortized cost, 5 to 10 years	0
Amortized cost, more than 10 years	0
Amortized Cost	29,993	52,411
Fair Value
Fair value, within one year	0
Fair value, 1 to 5 years	28,940
Fair value, 5 to 10 years	0
Fair value, more than 10 years	0
Total fair value	28,940	48,798
Mortgage-backed securities issued by U.S. Government agencies
Amortized Cost
Amortized cost, within one year	0
Amortized cost, 1 to 5 years	65
Amortized cost, 5 to 10 years	3
Amortized cost, more than 10 years	1,021,544
Amortized Cost	1,021,612	904,593
Fair Value
Fair value, within one year	0
Fair value, 1 to 5 years	63
Fair value, 5 to 10 years	3
Fair value, more than 10 years	925,598
Total fair value	925,664	792,749
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Amortized Cost
Amortized cost, within one year	0
Amortized cost, 1 to 5 years	0
Amortized cost, 5 to 10 years	11,063
Amortized cost, more than 10 years	7,512,336
Amortized Cost	7,523,399	8,144,374
Fair Value
Fair value, within one year	0
Fair value, 1 to 5 years	0
Fair value, 5 to 10 years	10,341
Fair value, more than 10 years	6,420,038
Total fair value	6,430,379	6,895,070
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Amortized Cost
Amortized cost, within one year	0
Amortized cost, 1 to 5 years	50
Amortized cost, 5 to 10 years	10,508
Amortized cost, more than 10 years	681,929
Amortized Cost	692,487	769,498
Fair Value
Fair value, within one year	0
Fair value, 1 to 5 years	49
Fair value, 5 to 10 years	10,220
Fair value, more than 10 years	577,326
Total fair value	587,595	655,127
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Amortized Cost
Amortized cost, within one year	66,599
Amortized cost, 1 to 5 years	545,350
Amortized cost, 5 to 10 years	597,302
Amortized cost, more than 10 years	17,421
Amortized Cost	1,226,672	877,590
Fair Value
Fair value, within one year	67,822
Fair value, 1 to 5 years	544,620
Fair value, 5 to 10 years	582,238
Fair value, more than 10 years	15,103
Total fair value	1,209,783	805,945
Corporate debt securities and other debt securities
Amortized Cost
Amortized cost, within one year	0
Amortized cost, 1 to 5 years	9,009
Amortized cost, 5 to 10 years	0
Amortized cost, more than 10 years	0
Amortized Cost	9,009	8,908
Fair Value
Fair value, within one year	0
Fair value, 1 to 5 years	8,672
Fair value, 5 to 10 years	0
Fair value, more than 10 years	0
Total fair value	$ 8,672	$ 8,601