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Investment Securities (Fair Value and Gross Unrealized Loss) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2020
Available for sale: |  |
Fair value, less than 12 months |  | $ 1,462,232
Marketable securities, less than 12 months | $ 523,797 |
Unrealized losses, less than 12 Months |  | (9,339)
Marketable securities, less than 12 Months | (2,274) |
Fair value, 12 months or more |  | 757
Marketable securities, 12 months or more | 1,448,109 |
Unrealized losses, 12 Months or More |  | (14)
Marketable securities, 12 Months or More | (14,340) |
Fair value, Total |  | 1,462,989
Marketable securities, Total | 1,971,906 |
Unrealized losses, Total |  | (9,353)
Marketable securities, Total | 16,614 |
Collateralized Mortgage Backed Securities [Member] |  |
Available for sale: |  |
Fair value, less than 12 months | 523,031 | 1,462,232
Unrealized losses, less than 12 Months | (2,269) | (9,339)
Fair value, 12 months or more | 1,448,109 |
Unrealized losses, 12 Months or More | (14,340) |
Fair value, Total | 1,971,140 | 1,462,232
Unrealized losses, Total | (16,609) | (9,339)
US States and Political Subdivisions Debt Securities [Member] |  |
Available for sale: |  |
Fair value, less than 12 months | 766 |
Unrealized losses, less than 12 Months | (5) |
Fair value, 12 months or more |  | 757
Unrealized losses, 12 Months or More |  | (14)
Fair value, Total | 766 | 757
Unrealized losses, Total | $ (5) | $ (14)

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