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Investments in Unconsolidated Entities - Narrative (Details) - USD ($) | 3 Months Ended | 7 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2019 | Mar. 31, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2019 | Sep. 30, 2018 | Feb. 26, 2019 | Dec. 31, 2018
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |
Ownership interest (as a percent) | 50.00% |  |  | 50.00% | 50.00% |  |  | 50.00%
Total revenues | $ 155,500,000 |  | $ 198,700,000 |  | $ 718,100,000 | $ 363,100,000 |  |
Total assets | 3,836,300,000 |  |  | $ 3,836,300,000 | 3,836,300,000 |  |  | $ 3,362,600,000
Total liabilities | 765,400,000 |  |  | 765,400,000 | 765,400,000 |  |  | 644,400,000
MediaAlpha |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  | 48.30% |
Fully diluted ownership interest (as a percent) |  |  |  |  |  |  | 42.00% |
Assets, fair value |  | $ 114,700,000 |  |  |  |  |  |
Unrealized investment gain | 35,300,000 | $ 114,700,000 |  |  | 150,000,000.0 |  |  |
Total assets | 0 |  |  | 0 | 0 |  |  | 88,400,000
Total liabilities | 0 |  |  | 0 | 0 |  |  | $ 46,900,000
MediaAlpha |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |
Total revenues | 0 |  | $ 74,500,000 |  | 48,800,000 | $ 218,000,000.0 |  |
MediaAlpha | MediaAlpha |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |
Total revenues | 110,500,000 |  |  | 233,200,000 |  |  |  |
Expenses | 102,100,000 |  |  | 217,900,000 |  |  |  |
Gross profit | 18,400,000 |  |  | 38,800,000 |  |  |  |
Pre-tax income | 8,400,000 |  |  | 15,300,000 |  |  |  |
Total assets | 103,400,000 |  |  | 103,400,000 | 103,400,000 |  |  |
Total liabilities | $ 145,800,000 |  |  | $ 145,800,000 | $ 145,800,000 |  |  |

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