Non-controlling Interest (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (142.6)	$ (131.7)
Total Non-Controlling Excluding Reciprocals
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 46.4	$ 31.5
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 15.4	$ 15.9
NSM Holding Co LLC
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	5.00%	0.00%
Total non-controlling interests	$ 14.3	$ 0.0
MediaAlpha
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	37.70%	35.70%
Total non-controlling interests	$ 14.8	$ 13.1
Buzzmove
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	22.90%	22.90%
Total non-controlling interests	$ 1.9	$ 2.5
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (189.0)	$ (163.2)