Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	$ 532.6	$ 440.5
OneBeacon [Member] | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	272.9	272.9
OneBeacon [Member] | Book Value | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	272.9	272.9
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	278.0	276.4
Tranzact [Member] | Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Long-term Line of Credit	94.1	104.7
Tranzact [Member] | Book Value | Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	92.4	102.9
Tranzact [Member] | Estimate of Fair Value Measurement [Member] | Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	92.8	102.8
MediaAlpha [Member] | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	2.5
Long-term Line of Credit	17.5	15.0
MediaAlpha [Member] | Book Value | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	17.2	14.7
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	$ 15.1	$ 15.0