Investment Securities Available for Sale (Schedule of Amortized Cost and Estimated Fair Value by Contractual Maturity of Investment Securities Available for Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Amortized Cost
Within one year, amortized cost	$ 25,140
1 to 5 years, amortized cost	1,206,162
5 to 10 years, amortized cost	353,060
More than 10 years, amortized cost	9,589,511
Amortized Cost	11,173,873	$ 11,273,327
Fair Value
Within one year, fair value	25,139
1 to 5 years, fair value	1,128,740
5 to 10 years, fair value	304,535
More than 10 years, fair value	8,162,761
Total, fair value	9,621,175	9,678,103
U.S. Treasury securities
Amortized Cost
Within one year, amortized cost	24,834
1 to 5 years, amortized cost	442,928
5 to 10 years, amortized cost	49,864
More than 10 years, amortized cost	0
Amortized Cost	517,626	515,953
Fair Value
Within one year, fair value	24,834
1 to 5 years, fair value	408,618
5 to 10 years, fair value	40,438
More than 10 years, fair value	0
Total, fair value	473,890	471,813
U.S. Government agency securities
Amortized Cost
Within one year, amortized cost	258
1 to 5 years, amortized cost	52,139
5 to 10 years, amortized cost	0
More than 10 years, amortized cost	0
Amortized Cost	52,397	52,411
Fair Value
Within one year, fair value	258
1 to 5 years, fair value	48,345
5 to 10 years, fair value	0
More than 10 years, fair value	0
Total, fair value	48,603	48,798
Mortgage-backed securities issued by U.S. Government agencies
Amortized Cost
Within one year, amortized cost	48
1 to 5 years, amortized cost	324
5 to 10 years, amortized cost	4
More than 10 years, amortized cost	927,655
Amortized Cost	928,031	904,593
Fair Value
Within one year, fair value	47
1 to 5 years, fair value	311
5 to 10 years, fair value	4
More than 10 years, fair value	816,988
Total, fair value	817,350	792,749
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Amortized Cost
Within one year, amortized cost	0
1 to 5 years, amortized cost	19,900
5 to 10 years, amortized cost	82,822
More than 10 years, amortized cost	7,876,409
Amortized Cost	7,979,131	8,144,374
Fair Value
Within one year, fair value	0
1 to 5 years, fair value	18,789
5 to 10 years, fair value	76,538
More than 10 years, fair value	6,682,066
Total, fair value	6,777,393	6,895,070
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	69
5 to 10 years, amortized cost	11,416
More than 10 years, amortized cost	721,453
Amortized Cost	732,938	769,498
Fair Value
Within one year, fair value	0
1 to 5 years, fair value	66
5 to 10 years, fair value	10,936
More than 10 years, fair value	604,949
Total, fair value	615,951	655,127
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	681,844
5 to 10 years, amortized cost	208,954
More than 10 years, amortized cost	63,994
Amortized Cost	954,792	877,590
Fair Value
Within one year, fair value	0
1 to 5 years, fair value	643,973
5 to 10 years, fair value	176,619
More than 10 years, fair value	58,758
Total, fair value	879,350	805,945
Corporate debt securities and other debt securities
Amortized Cost
Within one year, amortized cost	0
1 to 5 years, amortized cost	8,958
5 to 10 years, amortized cost	0
More than 10 years, amortized cost	0
Amortized Cost	8,958	8,908
Fair Value
Within one year, fair value	0
1 to 5 years, fair value	8,638
5 to 10 years, fair value	0
More than 10 years, fair value	0
Total, fair value	$ 8,638	$ 8,601

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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