Investment Securities Available for Sale (Amortized Cost and Estimated Fair Value by Contractual Maturity of Investment Securities Available for Sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Amortized Cost
Within one year, amortized cost	$ 33,873
1 to 5 years, amortized cost	907,287
5 to 10 years, amortized cost	582,969
More than 10 years, amortized cost	9,752,567
Amortized Cost	11,276,696	$ 10,991,506
Fair Value
Within one year, fair value	33,830
1 to 5 years, fair value	843,275
5 to 10 years, fair value	520,266
More than 10 years, fair value	8,190,137
Total, fair value	9,587,508	10,918,329
U.S. Treasury securities
Amortized Cost
Within one year, amortized cost	24,100
1 to 5 years, amortized cost	392,854
5 to 10 years, amortized cost	98,236
More than 10 years, amortized cost	0
Amortized Cost	515,190	120,465
Fair Value
Within one year, fair value	24,100
1 to 5 years, fair value	358,045
5 to 10 years, fair value	85,611
More than 10 years, fair value	0
Total, fair value	467,756	117,838
U.S. Government agency securities
Amortized Cost
Within one year, amortized cost	273
1 to 5 years, amortized cost	22,148
5 to 10 years, amortized cost	29,990
More than 10 years, amortized cost	0
Amortized Cost	52,411	53,214
Fair Value
Within one year, fair value	273
1 to 5 years, fair value	19,415
5 to 10 years, fair value	28,882
More than 10 years, fair value	0
Total, fair value	48,570	54,201
Mortgage-backed securities issued by U.S. Government agencies
Amortized Cost
Within one year, amortized cost	0
1 to 5 years, amortized cost	621
5 to 10 years, amortized cost	4
More than 10 years, amortized cost	840,110
Amortized Cost	840,735	790,329
Fair Value
Within one year, fair value	0
1 to 5 years, fair value	597
5 to 10 years, fair value	4
More than 10 years, fair value	722,011
Total, fair value	722,612	779,633
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Amortized Cost
Within one year, amortized cost	0
1 to 5 years, amortized cost	5,062
5 to 10 years, amortized cost	115,479
More than 10 years, amortized cost	8,054,100
Amortized Cost	8,174,641	8,063,890
Fair Value
Within one year, fair value	0
1 to 5 years, fair value	4,706
5 to 10 years, fair value	107,107
More than 10 years, fair value	6,721,126
Total, fair value	6,832,939	8,012,301
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Amortized Cost
Within one year, amortized cost	0
1 to 5 years, amortized cost	102
5 to 10 years, amortized cost	0
More than 10 years, amortized cost	791,208
Amortized Cost	791,310	951,691
Fair Value
Within one year, fair value	0
1 to 5 years, fair value	100
5 to 10 years, fair value	0
More than 10 years, fair value	684,408
Total, fair value	684,508	939,623
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Amortized Cost
Within one year, amortized cost	0
1 to 5 years, amortized cost	486,500
5 to 10 years, amortized cost	330,378
More than 10 years, amortized cost	67,149
Amortized Cost	884,027	479,420
Fair Value
Within one year, fair value	0
1 to 5 years, fair value	460,412
5 to 10 years, fair value	289,991
More than 10 years, fair value	62,592
Total, fair value	812,995	481,744
Corporate debt securities and other debt securities
Amortized Cost
Within one year, amortized cost	9,500
1 to 5 years, amortized cost	0
5 to 10 years, amortized cost	8,882
More than 10 years, amortized cost	0
Amortized Cost	18,382	18,309
Fair Value
Within one year, fair value	9,457
1 to 5 years, fair value	0
5 to 10 years, fair value	8,671
More than 10 years, fair value	0
Total, fair value	$ 18,128	$ 18,801

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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