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Investment Securities (Net Realized and Unrealized Investment Gains (Losses)) (Details) - USD ($) | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Mar. 31, 2019 | Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |  |
Trading Securities, Realized and Unrealized Gain (Loss) | $ 2,200,000 | $ 200,000 |  | $ (6,500,000) | $ 12,400,000 |
MediaAlpha |  |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |  |
Trading Securities, Realized and Unrealized Gain (Loss) |  |  |  |  | 67,500,000 |
Unrealized investment gain | 15,000,000.0 |  | $ 114,700,000 | $ 45,000,000.0 | $ 114,700,000 | $ 180,000,000.0
Foreign Currency Gain (Loss) |  |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |  |
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax | $ 400,000 | $ 300,000 |  |  |  |

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