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Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Equity Securities: |  |
Fair Value | $ 10,218 | $ 11,250
Debt Securities: |  |
Fair Value | 101,683 | 76,733
Cost Amount | 114,398 | 88,570
Gross Unrealized Gains | 126 | 568
Gross Unrealized (Losses) | (2,623) | (1,155)
Fair Value | 111,901 | 87,983
SEI-sponsored mutual funds |  |
Equity Securities: |  |
Cost Amount | 7,446 | 7,369
Gross Unrealized Gains | 0 | 110
Gross Unrealized (Losses) | (788) | (143)
Fair Value | 6,658 | 7,336
Equities and other mutual funds |  |
Equity Securities: |  |
Cost Amount | 3,434 | 3,456
Gross Unrealized Gains | 126 | 458
Gross Unrealized (Losses) | 0 | 0
Fair Value | 3,560 | 3,914
Debt securities |  |
Debt Securities: |  |
Cost Amount | 103,518 | 77,745
Gross Unrealized Gains | 0 | 0
Gross Unrealized (Losses) | (1,835) | (1,012)
Fair Value | $ 101,683 | $ 76,733

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