Non-controlling Interest (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (143.2)	$ (131.7)	$ 131.5
Total Non-Controlling Excluding Reciprocals
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 34.3	$ 31.5
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 15.7	$ 15.9
MediaAlpha
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	37.70%	35.70%
Total non-controlling interests	$ 16.2	$ 13.1
Buzzmove
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	22.90%	22.90%
Total non-controlling interests	$ 2.4	$ 2.5
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (177.5)	$ (163.2)