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Debt Securities - AFS Debt Securities in an Unrealized Loss Position (Details) $ in Thousands | Sep. 30, 2021 USD ($) security | Dec. 31, 2020 USD ($) security
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Available-for-sale |  |
Number of available-for-sale securities | security | 174 | 46
Less than 12 months, fair value | $ 3,885,154 | $ 145,530
Less than 12 months, unrealized loss | (22,568) | (783)
12 months or more, fair value | 121,504 | 753
12 months or more, unrealized loss | (3,048) | (9)
Total, fair value | 4,006,658 | 146,283
Total, unrealized loss | $ (25,616) | $ (792)
Held-to-maturity |  |
Number of held-to-maturity securities | security | 126 |
Less than 12 Months | $ 317,479 |
Less than 12 Months | (1,977) |
12 Months or More | 0 |
12 Months or More | 0 |
Total, fair value | 317,479 |
Total, unrealized loss | $ (1,977) |
U.S. government and federal agency |  |
Available-for-sale |  |
Number of available-for-sale securities | security | 23 | 18
Less than 12 months, fair value | $ 9,736 | $ 13,814
Less than 12 months, unrealized loss | (78) | (258)
12 months or more, fair value | 5,398 | 726
12 months or more, unrealized loss | (205) | (9)
Total, fair value | 15,134 | 14,540
Total, unrealized loss | $ (283) | $ (267)
U.S. government sponsored enterprises |  |
Available-for-sale |  |
Number of available-for-sale securities | security | 3 |
Less than 12 months, fair value | $ 45,279 |
Less than 12 months, unrealized loss | (279) |
12 months or more, fair value | 0 |
12 months or more, unrealized loss | 0 |
Total, fair value | 45,279 |
Total, unrealized loss | $ (279) |
State and local governments |  |
Available-for-sale |  |
Number of available-for-sale securities | security | 11 | 6
Less than 12 months, fair value | $ 15,596 | $ 3,121
Less than 12 months, unrealized loss | (30) | (54)
12 months or more, fair value | 1,742 | 0
12 months or more, unrealized loss | (61) | 0
Total, fair value | 17,338 | 3,121
Total, unrealized loss | $ (91) | $ (54)
Held-to-maturity |  |
Number of held-to-maturity securities | security | 126 |
Less than 12 Months | $ 317,479 |
Less than 12 Months | (1,977) |
12 Months or More | 0 |
12 Months or More | 0 |
Total, fair value | 317,479 |
Total, unrealized loss | $ (1,977) |
Corporate bonds |  |
Available-for-sale |  |
Number of available-for-sale securities | security | 1 | 3
Less than 12 months, fair value | $ 5,016 | $ 5,500
Less than 12 months, unrealized loss | (3) | (8)
12 months or more, fair value | 0 | 0
12 months or more, unrealized loss | 0 | 0
Total, fair value | 5,016 | 5,500
Total, unrealized loss | $ (3) | $ (8)
Residential mortgage-backed securities |  |
Available-for-sale |  |
Number of available-for-sale securities | security | 115 | 14
Less than 12 months, fair value | $ 3,730,195 | $ 2,354
Less than 12 months, unrealized loss | (21,312) | (4)
12 months or more, fair value | 26 | 27
12 months or more, unrealized loss | (1) | 0
Total, fair value | 3,730,221 | 2,381
Total, unrealized loss | $ (21,313) | $ (4)
Commercial mortgage-backed securities |  |
Available-for-sale |  |
Number of available-for-sale securities | security | 21 | 5
Less than 12 months, fair value | $ 79,332 | $ 120,741
Less than 12 months, unrealized loss | (866) | (459)
12 months or more, fair value | 114,338 | 0
12 months or more, unrealized loss | (2,781) | 0
Total, fair value | 193,670 | 120,741
Total, unrealized loss | $ (3,647) | $ (459)

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