Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	$ 285.9	$ 337.6
OneBeacon | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	273.2	272.9
OneBeacon | Fair value | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	274.2	276.4
OneBeacon | Carrying Value | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	273.2	272.9
MediaAlpha [Member] | Fair value | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	13.0	15.0
MediaAlpha [Member] | Carrying Value | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	$ 12.7	$ 14.7