Goodwill and Other Intangible Assets (Goodwill and Intangible Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Aug. 04, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 14, 2014	Feb. 19, 2014
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 58.6		$ 53.6
Amortization of Intangible Assets	34.4		22.3
Intangible Assets, Net (Excluding Goodwill)	24.2		31.3	$ 38.7
Goodwill	31.7		24.1	$ 23.8
Intangible Assets, Gross (Including Goodwill)	90.3		77.7
Goodwill and intangible assets	55.9		55.4
MediaAlpha
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	42.4		38.5
Amortization of Intangible Assets	24.1		14.1
Intangible Assets, Net (Excluding Goodwill)	18.3		24.4		$ 38.5
Goodwill	18.3		18.3		$ 18.3
WOBI [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	5.7		5.7
Amortization of Intangible Assets	2.0		1.2
Intangible Assets, Net (Excluding Goodwill)	3.7		4.5
Goodwill	5.8		5.8			$ 5.5
Buzzmove [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	1.1		0.0
Amortization of Intangible Assets	0.1		0.0
Intangible Assets, Net (Excluding Goodwill)	1.0	$ 1.1	0.0
Goodwill	7.6	$ 7.6	0.0
Developed Technology Rights [Member] | MediaAlpha
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	32.4		32.0
Amortization of Intangible Assets	17.9		11.2
Intangible Assets, Net (Excluding Goodwill)	$ 14.5		20.8
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years
Developed Technology Rights [Member] | WOBI [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 3.6		3.6
Amortization of Intangible Assets	1.2		0.7
Intangible Assets, Net (Excluding Goodwill)	$ 2.4		2.9
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years
Developed Technology Rights [Member] | Buzzmove [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 0.5		0.0
Amortization of Intangible Assets	0.0		0.0
Intangible Assets, Net (Excluding Goodwill)	$ 0.5		0.0
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years
Customer Relationships [Member] | MediaAlpha
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 10.0		6.5
Amortization of Intangible Assets	6.2		2.9
Intangible Assets, Net (Excluding Goodwill)	$ 3.8		3.6
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	3 years
Trademarks [Member] | WOBI [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 2.1		2.1
Amortization of Intangible Assets	0.8		0.5
Intangible Assets, Net (Excluding Goodwill)	$ 1.3		1.6
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	8 years
Trademarks [Member] | Buzzmove [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 0.6		0.0
Amortization of Intangible Assets	0.1		0.0
Intangible Assets, Net (Excluding Goodwill)	$ 0.5		0.0
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years
Other Intangible Assets [Member] | OneBeacon
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 9.4		9.4
Amortization of Intangible Assets	8.2		7.0
Intangible Assets, Net (Excluding Goodwill)	$ 1.2		$ 2.4
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years