Amount of debt issuance costs (for example, but not limited to, legal, accounting, broker, and regulatory fees).

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
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-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 11
-Article 7

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- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Subparagraph (a),(b)
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-Name Accounting Standards Codification
-Glossary Income Tax Expense (or Benefit)
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- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

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- Definition

Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 16
-Article 12

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- Definition

The cash outflow associated with the acquisition of a controlling interest in another entity or an entity that is related to it but not strictly controlled (for example, an unconsolidated subsidiary, affiliate, joint venture or equity method investment).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
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-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

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- Definition

Financial instruments issued by insurance entities (surplus notes) that are includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations that are liabilities of the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6486086&loc=d3e24387-158525

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No definition available.

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- Definition

Percentage of par value of policy reinsured.

+ References

No definition available.

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Summary of Significant Accounting Policies (Basis of Presentation) (Details) £ in Millions, $ in Millions			3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 04, 2016 GBP (£)	Aug. 04, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Jul. 31, 2012 USD ($)
Basis of Presentation
Debt Issuance Cost					$ 1.9
Net investment income			$ 22.5	$ 16.8	59.6	$ 42.6
Income Tax Expense (Benefit)			(6.7)	(1.6)	(22.4)	0.8
Equity in earnings of unconsolidated affiliates, net of tax			$ 0.0	$ 3.9	0.0	18.0
Payments to Acquire Businesses and Interest in Affiliates					$ 13.7	$ 2.4
OneBeacon Ltd.
Basis of Presentation
Ownership interest (as a percent)			76.10%		76.10%		75.50%
HG Global
Basis of Presentation
Surplus Notes								$ 503.0
Percentage of par value of policy reinsured			15.00%		15.00%
Noncontrolling equity percentage			3.10%		3.10%		3.10%
Buzzmove [Member]
Basis of Presentation
Ownership interest (as a percent)	70.90%	70.90%
Noncontrolling equity percentage			29.10%		29.10%		0.00%
Star & Shield Insurance Exchange
Basis of Presentation
Noncontrolling equity percentage			100.00%		100.00%		100.00%
OneBeacon [Member]
Basis of Presentation
Debt Issuance Cost							$ 1.9
Noncontrolling equity percentage			23.90%		23.90%		24.50%
Preferred Stock \| HG Global
Basis of Presentation
Ownership interest (as a percent)			96.90%		96.90%
Noncontrolling equity percentage			96.90%		96.90%		96.90%
Common Stock \| HG Global
Basis of Presentation
Ownership interest (as a percent)			88.40%		88.40%
Noncontrolling equity percentage			88.40%		88.40%		88.40%
United Kingdom, Pounds \| Buzzmove [Member]
Basis of Presentation
Payments to Acquire Businesses and Interest in Affiliates	£ 6.0	$ 6.0
United States of America, Dollars \| Buzzmove [Member]
Basis of Presentation
Payments to Acquire Businesses and Interest in Affiliates		$ 8.0