Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	$ 284.7	$ 285.9
OneBeacon [Member] | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	273.2	273.2
OneBeacon [Member] | Book Value | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	273.2	273.2
OneBeacon [Member] | Estimate of Fair Value Measurement [Member] | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	279.4	274.2
MediaAlpha [Member] | Book Value | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	11.5	12.7
MediaAlpha [Member] | Estimate of Fair Value Measurement [Member] | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	$ 11.7	$ 13.0