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Discontinued Operations Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2014 | Mar. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements | 125,000 | 125,000
Basic and diluted (loss) earnings per share numerators (in millions): |  |
Income (Loss) Allocated to Participating Unvested Restricted Common Shares | $ (1.1) | $ (1.5)
Net income attributable to White Mountains' common shareholders, net of restricted common share amounts | 95.6 | 120.4
Basic (loss) earnings per share denominators (in thousands): |  |
Total average common shares outstanding during the period | 6,169,900 | 6,273,500
Average unvested restricted common shares | (70,400) | (79,000)
Basic (loss) earnings per share denominator | 6,099,500 | 6,194,500
Diluted (loss) earnings per share denominator (in thousands): |  |
Total average common shares outstanding during the period | 6,169,900 | 6,273,500
Average unvested restricted common shares | (70,400) | (79,000)
Average outstanding dilutive options to acquire common shares | 0 | 0
Diluted (loss) earnings per share denominator | 6,099,500 | 6,194,500
Segment, Discontinued Operations |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements | 125,000 | 125,000
Basic and diluted (loss) earnings per share numerators (in millions): |  |
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent | (0.5) | 0.5
Income (Loss) Allocated to Participating Unvested Restricted Common Shares | 0 | 0
Net income attributable to White Mountains' common shareholders, net of restricted common share amounts | $ (0.5) | $ 0.5
Basic (loss) earnings per share denominators (in thousands): |  |
Total average common shares outstanding during the period | 6,169,900 | 6,273,500
Average unvested restricted common shares | (70,400) | (79,000)
Basic (loss) earnings per share denominator | 6,099,500 | 6,194,500
Diluted (loss) earnings per share denominator (in thousands): |  |
Total average common shares outstanding during the period | 6,169,900 | 6,273,500
Average unvested restricted common shares | (70,400) | (79,000)
Average outstanding dilutive options to acquire common shares | 0 | 0
Diluted (loss) earnings per share denominator | 6,099,500 | 6,194,500
Basic and diluted (loss) earnings per share (in dollars): | $ (0.08) | $ 0.07

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- Definition The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. + References No definition available. + Details
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- Definition Amount of income (loss) from a disposal group, net of income tax, reported as a separate component of income before extraordinary items after deduction or consideration of the amount allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569616-111683 + Details
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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 Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1377-109256 + Details
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- Definition The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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