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Debt (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Nov. 30, 2012 | Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2012 | Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2015 | Jul. 23, 2015 | Aug. 14, 2013
Debt Instrument |  |  |  |  |  |  |  |  |
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements |  | 11,943 |  |  | 8,208 |  |  |  |
Total debt |  | $ 288.5 |  |  | $ 288.5 |  | $ 337.6 |  |
Repayments of Debt |  |  |  |  | 401.8 | $ 84.5 |  |  |
Draw down of debt and revolving line of credit |  |  |  |  | $ 352.5 | $ 98.5 |  |  |
MediaAlpha Bank Facility [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Basis Spread on Variable Rate |  |  |  |  | 1.50% |  |  |  |
2012 OBH Senior Notes |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  |  | $ 275.0 |  |  |  |  |
WTM Bank Facility |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  |  |  |  |  |  | 3.90% |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  | $ 425.0
Debt, Weighted Average Interest Rate |  | 3.85% |  |  | 3.85% |  |  |  |
Repayments of Debt |  | $ 250.0 |  |  | $ 400.0 |  |  |  |
Proceeds from Issuance of Debt |  |  | $ 250.0 |  | 350.0 |  |  |  |
Term Loan [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Repayments of Debt |  | 0.8 |  |  | 0.8 |  |  |  |
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Repayments of Debt |  | 0.5 |  |  | 1.0 |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  | 2.5 |  |  |  |
OB Bank Facility [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  | 65.0 |  |  | 65.0 |  |  |  |
One Beacon Holdings Inc [Member] | 2012 OBH Senior Notes |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 4.70% |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt | $ 272.9 |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.60% |  |  |  |  |  |  |  |
Debt Instrument, Issue Price as Percentage of Par Value | 99.90% |  |  |  |  |  |  |  |
OneBeacon [Member] | OneBeacon Bank Facility [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Long-term Line of Credit |  | 0.0 |  |  | 0.0 |  |  |  |
OneBeacon [Member] | 2012 OBH Senior Notes |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt instrument at face value |  | 275.0 |  |  | 275.0 |  | $ 275.0 |  |
Unamortized original issue discount |  | (1.9) |  |  | (1.9) |  | (2.1) |  |
Total debt |  | $ 273.1 |  |  | $ 273.1 |  | $ 272.9 |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 4.70% |  |  | 4.70% |  | 4.70% |  |
White Mountains | WTM Bank Facility |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Total debt |  | $ 0.0 |  |  | $ 0.0 |  | $ 50.0 |  |
Tranzact [Member] | OneBeacon Bank Facility [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Long-term Line of Credit |  |  |  |  |  |  | 0.0 |  |
MediaAlpha [Member] | MediaAlpha Bank Facility [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Total debt |  | 1.5 |  |  | 1.5 |  |  |  |
Long-term Line of Credit |  | $ 15.6 |  |  | $ 15.6 |  | $ 15.0 |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 5.80% |  |  | 5.80% |  | 5.50% |  |
Unamortized Debt Issuance Expense |  | $ (0.2) |  |  | $ (0.2) |  | $ (0.3) |  |
Line of Credit Facility, Fair Value of Amount Outstanding |  | 15.4 |  |  | 15.4 |  | $ 14.7 |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  | $ 20.0 |
Notional amount |  | 14.2 |  |  | 14.2 |  |  |  |
Line of Credit Facility, Remaining Borrowing Capacity |  | 5.0 |  |  | 5.0 |  |  |  |
Failure to pay principal and interest [Member] | OneBeacon [Member] | 2012 OBH Senior Notes |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Total debt |  | $ 75.0 |  |  | $ 75.0 |  |  |  |

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- Definition Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 28A -URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1500-109256 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 + Details
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