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Equity-Method Eligible Investments - Narrative (Details) - USD ($) | 3 Months Ended | 10 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Feb. 26, 2019
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 175,300,000 | $ 155,500,000 | $ 129,000,000.0 | $ 433,600,000 | $ 6,000,000.0 | $ 198,700,000 | $ 122,300,000 | $ 42,100,000 |  | $ 893,400,000 | $ 369,100,000 | $ 373,800,000 |
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 |  |  |  | $ 114,700,000 |  |  |  |  |  | 180,000,000.0 |  |  |
MediaAlpha |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | $ 48,800,000 | $ 297,100,000 | $ 163,200,000 |
MediaAlpha | MediaAlpha |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | $ 359,200,000 |  |  |  |
Expenses |  |  |  |  |  |  |  |  | 334,300,000 |  |  |  |
Gross profit |  |  |  |  |  |  |  |  | 59,700,000 |  |  |  |
Pre-tax income |  |  |  |  |  |  |  |  | $ 24,900,000 |  |  |  |

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