Investment Securities (Net Realized and Unrealized Investment Gains (Losses) (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net realized investment gains (losses), pre-tax (1)	$ 19,600,000		$ (10,200,000)	$ 90,800,000	$ (13,900,000)
Net unrealized investment gains (losses), pre-tax	47,400,000		76,300,000	257,000,000.0	36,800,000
Net realized and unrealized investment gains, pre-tax	67,000,000.0		66,100,000	347,800,000	22,900,000
Income tax expense attributable to net realized and unrealized investment gains	(13,200,000)		(9,700,000)	(69,500,000)	(5,900,000)
Net realized and unrealized investment gains, after-tax	53,800,000		$ 56,400,000	278,300,000	17,000,000.0
Net gain from sale of discontinued operations, net of tax				67,500,000	$ 0
MediaAlpha
Net gain from sale of discontinued operations, net of tax				67,500,000
Unrealized investment gain	$ 35,300,000	$ 114,700,000		$ 150,000,000.0