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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 | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Amortized Cost |  |
Within one year, amortized cost | $ 55,106 |
1 to 5 years, amortized cost | 1,286,444 |
5 to 10 years, amortized cost | 346,639 |
More than 10 years, amortized cost | 9,486,566 |
Amortized Cost | 11,174,755 | $ 11,273,327
Fair Value |  |
Within one year, fair value | 54,363 |
1 to 5 years, fair value | 1,201,659 |
5 to 10 years, fair value | 291,498 |
More than 10 years, fair value | 7,689,671 |
Total, fair value | 9,237,191 | 9,678,103
U.S. Treasury securities |  |
Amortized Cost |  |
Within one year, amortized cost | 25,352 |
1 to 5 years, amortized cost | 481,570 |
5 to 10 years, amortized cost | 49,869 |
More than 10 years, amortized cost | 0 |
Amortized Cost | 556,791 | 515,953
Fair Value |  |
Within one year, fair value | 25,352 |
1 to 5 years, fair value | 445,205 |
5 to 10 years, fair value | 38,903 |
More than 10 years, fair value | 0 |
Total, fair value | 509,460 | 471,813
U.S. Government agency securities |  |
Amortized Cost |  |
Within one year, amortized cost | 0 |
1 to 5 years, amortized cost | 52,140 |
5 to 10 years, amortized cost | 0 |
More than 10 years, amortized cost | 0 |
Amortized Cost | 52,140 | 52,411
Fair Value |  |
Within one year, fair value | 0 |
1 to 5 years, fair value | 47,506 |
5 to 10 years, fair value | 0 |
More than 10 years, fair value | 0 |
Total, fair value | 47,506 | 48,798
Mortgage-backed securities issued by U.S. Government agencies |  |
Amortized Cost |  |
Within one year, amortized cost | 36 |
1 to 5 years, amortized cost | 267 |
5 to 10 years, amortized cost | 4 |
More than 10 years, amortized cost | 1,040,518 |
Amortized Cost | 1,040,825 | 904,593
Fair Value |  |
Within one year, fair value | 34 |
1 to 5 years, fair value | 257 |
5 to 10 years, fair value | 3 |
More than 10 years, fair value | 891,960 |
Total, fair value | 892,254 | 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 | 18,277 |
5 to 10 years, amortized cost | 78,557 |
More than 10 years, amortized cost | 7,684,917 |
Amortized Cost | 7,781,751 | 8,144,374
Fair Value |  |
Within one year, fair value | 0 |
1 to 5 years, fair value | 17,284 |
5 to 10 years, fair value | 70,862 |
More than 10 years, fair value | 6,173,606 |
Total, fair value | 6,261,752 | 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 | 58 |
5 to 10 years, amortized cost | 10,944 |
More than 10 years, amortized cost | 699,598 |
Amortized Cost | 710,600 | 769,498
Fair Value |  |
Within one year, fair value | 0 |
1 to 5 years, fair value | 56 |
5 to 10 years, fair value | 10,337 |
More than 10 years, fair value | 568,443 |
Total, fair value | 578,836 | 655,127
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises |  |
Amortized Cost |  |
Within one year, amortized cost | 29,718 |
1 to 5 years, amortized cost | 725,148 |
5 to 10 years, amortized cost | 207,265 |
More than 10 years, amortized cost | 61,533 |
Amortized Cost | 1,023,664 | 877,590
Fair Value |  |
Within one year, fair value | 28,977 |
1 to 5 years, fair value | 682,703 |
5 to 10 years, fair value | 171,393 |
More than 10 years, fair value | 55,662 |
Total, fair value | 938,735 | 805,945
Corporate debt securities and other debt securities |  |
Amortized Cost |  |
Within one year, amortized cost | 0 |
1 to 5 years, amortized cost | 8,984 |
5 to 10 years, amortized cost | 0 |
More than 10 years, amortized cost | 0 |
Amortized Cost | 8,984 | 8,908
Fair Value |  |
Within one year, fair value | 0 |
1 to 5 years, fair value | 8,648 |
5 to 10 years, fair value | 0 |
More than 10 years, fair value | 0 |
Total, fair value | $ 8,648 | $ 8,601

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