Investments in Unconsolidated Entities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		4 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Feb. 26, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Total revenues	$ 129.0	$ 122.3		$ 562.6	$ 164.4
Total assets	3,752.2		$ 3,752.2	3,752.2			$ 3,362.6
Total liabilities	744.3		744.3	744.3			644.4
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	114.7		114.7	114.7
Unrealized investment gain				114.7
Total assets	0.0		0.0	0.0			88.4
Total liabilities	0.0		0.0	0.0			$ 46.9
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Total revenues	0.0	$ 71.8		48.8	$ 143.5
MediaAlpha | MediaAlpha
Schedule of Equity Method Investments [Line Items]
Total revenues	89.1		122.7
Expenses	83.3		115.8
Pre-tax income	5.8		6.9
Total assets	107.4		107.4	107.4
Total liabilities	$ 152.9		$ 152.9	$ 152.9