Face (par) amount of debt instrument at time of issuance.

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The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

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Amount borrowed under the credit facility as of the balance sheet date.

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Fair value of the amount outstanding under the credit facility.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Number of Credit Lines

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Debt (Details) (USD $)	3 Months Ended
Debt (Details) (USD $)	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Aug. 14, 2013	Oct. 10, 2014	Nov. 25, 2014
Debt Instrument
Total debt	$ 749,800,000us-gaap_LongTermDebt		$ 746,600,000us-gaap_LongTermDebt
Repayments of Debt	1,300,000us-gaap_RepaymentsOfDebt	0us-gaap_RepaymentsOfDebt
Draw down of debt and revolving line of credit	4,500,000us-gaap_ProceedsFromLinesOfCredit	0us-gaap_ProceedsFromLinesOfCredit
2012 OBH Senior Notes
Debt Instrument
Total debt	291,500,000		286,000,000
WTM Bank Facility
Debt Instrument
Total commitment under revolving credit facility				425,000,000
Other Debt [Member]
Debt Instrument
Total debt	4,800,000		4,800,000
OneBeacon \| 2012 OBH Senior Notes
Debt Instrument
Debt instrument at face value	275,000,000		275,000,000
Unamortized original issue discount	(300,000)		(300,000)
Total debt	274,700,000		274,700,000
Sirius Group \| SIG Senior Notes
Debt Instrument
Debt instrument at face value	400,000,000		400,000,000
Unamortized original issue discount	(300,000)		(300,000)
Total debt	399,700,000		399,700,000
White Mountains \| WTM Bank Facility
Debt Instrument
Total debt	0		0
Tranzact [Member] \| Tranzact Bank Facility [Member]
Debt Instrument
Line of Credit Facility, Amount Outstanding	71,900,000		68,700,000
Unamortized Debt Issuance Expense	(1,300,000)		(1,300,000)
Line of Credit Facility, Fair Value of Amount Outstanding	70,600,000		67,400,000		70,000,000
Total commitment under revolving credit facility					74,500,000
Line of Credit Facility, Remaining Borrowing Capacity					4,500,000
Repayments of Debt	1,300,000
Draw down of debt and revolving line of credit	4,500,000
Sirius International [Member] \| Letter of Credit [Member]
Debt Instrument
number of Credit Lines						2
Line of Credit Facility, Fair Value of Amount Outstanding						200,000,000
Nordea Bank Finland
Debt Instrument
Total commitment under revolving credit facility						125,000,000.0
Lloyds Bank plc [Member]
Debt Instrument
Total commitment under revolving credit facility						75,000,000.0
Unsecured Debt [Member] \| Nordea Bank Finland
Debt Instrument
Total commitment under revolving credit facility						100,000,000.0
Unsecured Debt [Member] \| Lloyds Bank plc [Member]
Debt Instrument
Total commitment under revolving credit facility						$ 25,000,000.0