Investments in Unconsolidated Entities - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2019	Mar. 31, 2018	Feb. 26, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Total revenues		$ 433.6	$ 42.1
Total assets	$ 3,629.7	3,629.7			$ 3,362.6
Total liabilities	651.4	651.4			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
Unrealized investment gain		114.7
Total assets	0.0	0.0			88.4
Total liabilities	0.0	0.0			$ 46.9
MediaAlpha | MediaAlpha
Schedule of Equity Method Investments [Line Items]
Total revenues	33.5	48.8	$ 71.7
Expenses	32.5
Pre-tax income	1.1
Total assets	102.3	102.3
Total liabilities	$ 148.2	$ 148.2