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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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