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Investments in Marketable Securities - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Mar. 31, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Investments, Debt and Equity Securities [Abstract] |  |  |  |  |
Proceeds received from sales of marketable securities | $ 3.4 |  | $ 12.1 | $ 18.5 | $ 25.9
Net realized gains (losses) on sale of marketable securities | $ 0.2 |  | $ 1.3 | $ 0.7 | $ 4.1
Affiliate sponsored investment products |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Fair value of deconsolidated investment in affiliate |  | $ 84.3 |  |  |

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- Definition Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI). + References No definition available. + Details
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- Details
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