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Investment Securities (Fair Value and Gross Unrealized Loss) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2019
Available for sale: |  |
Fair value, less than 12 months |  | $ 523,797
Marketable securities, less than 12 months | $ 221,140 |
Unrealized losses, less than 12 Months |  | (2,274)
Marketable securities, less than 12 Months | (2,223) |
Fair value, 12 months or more |  | 1,448,109
Marketable securities, 12 months or more | 2,537,693 |
Unrealized losses, 12 Months or More |  | (14,340)
Marketable securities, 12 Months or More | (77,051) |
Fair value, Total |  | 1,971,906
Marketable securities, Total | 2,758,833 |
Unrealized losses, Total |  | (16,614)
Marketable securities, Total | 79,274 |
Residential mortgage-backed securities |  |
Available for sale: |  |
Fair value, less than 12 months | 208,384 | 523,031
Unrealized losses, less than 12 Months | (2,124) | (2,269)
Fair value, 12 months or more | 2,537,181 | 1,448,109
Unrealized losses, 12 Months or More | (77,045) | (14,340)
Fair value, Total | 2,745,565 | 1,971,140
Unrealized losses, Total | (79,169) | (16,609)
Obligations of states and political subdivisions |  |
Available for sale: |  |
Fair value, less than 12 months | 12,756 | 766
Unrealized losses, less than 12 Months | (99) | (5)
Fair value, 12 months or more | 512 |
Unrealized losses, 12 Months or More | (6) |
Fair value, Total | 13,268 | 766
Unrealized losses, Total | $ (105) | $ (5)

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