Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	$ 195.4	$ 192.7
NSM Holding Co LLC
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	184.5	178.5
NSM Holding Co LLC | NSM Bank Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	182.8	176.6
NSM Holding Co LLC | Carrying Value | NSM Bank Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	182.8	176.6
NSM Holding Co LLC | Estimate of Fair Value Measurement | NSM Bank Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt instrument, fair value disclosure	182.9	176.1
MediaAlpha
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	0.0	14.2
MediaAlpha | MediaAlpha Bank Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	0.0	14.2
MediaAlpha | Carrying Value | MediaAlpha Bank Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	0.0	14.2
MediaAlpha | Estimate of Fair Value Measurement | MediaAlpha Bank Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt instrument, fair value disclosure	0.0	14.6
Other Operations | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	10.9	0.0
Other Operations | Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt instrument, fair value disclosure	$ 10.9	$ 0.0