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Employee Share-Based Incentive Compensation Plans (Tables) | 3 Months Ended
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Mar. 31, 2017
White Mountains |
Share-based compensation arrangement by share-based payment award |
Summary of performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan | The following table summarizes performance share activity for the three months ended March 31, 2017 and 2016 for performance shares granted under the WTM Incentive Plan:
|  | Three Months Ended March 31,
|  | 2017 |  | 2016
Millions, except share amounts |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense
Beginning of period |  | 80,353 |  |  | $ | 42.4 |  |  | 93,654 |  |  | $ | 57.7 |
Shares paid or expired(1) |  | (30,167 | ) |  | (20.8 | ) |  | — |  |  | — |
New grants |  | 16,460 |  |  | — |  |  | 16,215 |  |  | — |
Forfeitures and cancellations(2) |  | (9,841 | ) |  | (5.7 | ) |  | (1,186 | ) |  | (.6 | )
Expense recognized |  | — |  |  | 8.1 |  |  | — |  |  | 14.2 |
End of period(3) |  | 56,805 |  |  | $ | 24.0 |  |  | 108,683 |  |  | $ | 71.3 |
(1) WTM performance share payments in 2017 for the 2014-2016 performance cycle, which were paid in March 2017, ranged from 34% to 76% of target. WTM performance share payments in 2016 for the 2013-2015 performance cycle ranged from 140% to 142% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP. (3) Outstanding performance share awards as of March 31, 2017 and 2016 exclude 2,195 and 10,826 performance share awards granted to employees of Sirius Group.
Share-based Compensation, Performance Shares Award Outstanding Activity [Table Text Block] | The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan at March 31, 2017 for each performance cycle:
Millions, except share amounts |  | Target Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |  |  |
2017 – 2019 |  | 16,460 |  |  | $ | 1.2 |
2016 – 2018 |  | 19,415 |  |  | 7.3 |
2015 – 2017 |  | 21,795 |  |  | 15.8 |
Sub-total |  | 57,670 |  |  | 24.3 |
Assumed forfeitures |  | (865 | ) |  | (.3 | )
March 31, 2017 |  | 56,805 |  |  | $ | 24.0 |
Summary of restricted shares activity | The following table summarizes the unrecognized compensation cost associated with the outstanding restricted share awards for the three months ended March 31, 2017 and 2016:
|  | Three Months Ended March 31,
|  | 2017 |  | 2016
Millions, except share amounts |  | Restricted Shares |  | Unamortized Issue Date Fair Value |  | Restricted Shares |  | Unamortized Issue Date Fair Value
Non-vested, |  |  |  |  |  |  |  |
Beginning of period |  | 70,620 |  |  | $ | 19.7 |  |  | 70,675 |  |  | $ | 15.7 |
Issued |  | 16,735 |  |  | 15.8 |  |  | 21,215 |  |  | 16.8 |
Vested |  | (22,015 | ) |  | — |  |  | (24,620 | ) |  | — |
Forfeited |  | (5,200 | ) |  | (2.8 | ) |  | (800 | ) |  | (.3 | )
Expense recognized |  | — |  |  | (3.6 | ) |  | — |  |  | (3.0 | )
End of period (1) |  | 60,140 |  |  | $ | 29.1 |  |  | 66,470 |  |  | $ | 29.2 |
(1) Restricted share awards outstanding as of March 31, 2017 and 2016 include 5,235 and 2,195 restricted shares issued to employees of Sirius Group, which was accounted for as discontinued operations.
OneBeacon [Member] |
Share-based compensation arrangement by share-based payment award |
Summary of performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan | The following table summarizes performance share activity for the three months ended March 31, 2017 and 2016 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:
|  | Three Months Ended March 31,
|  | 2017 |  | 2016
Millions, except share amounts |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense
Beginning of period |  | 452,519 |  |  | $ | 1.6 |  |  | 449,435 |  |  | $ | 1.4 |
Shares paid or expired(1) |  | (142,710 | ) |  | — |  |  | (167,300 | ) |  | (.7 | )
New grants |  | — |  |  | — |  |  | 163,150 |  |  | — |
Assumed forfeitures and cancellations(2) |  | (13 | ) |  | — |  |  | (4,079 | ) |  | — |
Expense recognized |  | — |  |  | .3 |  |  | — |  |  | .4 |
End of period |  | 309,796 |  |  | $ | 1.9 |  |  | 441,206 |  |  | $ | 1.1 |
(1) There were no payments made in 2017 for the 2014-2016 performance cycle; those performance shares did not meet the threshold performance goals and expired. OneBeacon performance share payments in 2016 for the 2013-2015 performance cycle were at 24.3% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP.
Share-based Compensation, Performance Shares Award Outstanding Activity [Table Text Block] | The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at March 31, 2017 for each performance cycle:
Millions, except share amounts |  | Target Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |  |  |
2016 – 2018 |  | 163,150 |  |  | $ | 1.1 |
2015 – 2017 |  | 146,646 |  |  | .8 |
Sub-total |  | 309,796 |  |  | 1.9 |
Assumed forfeitures |  | — |  |  | — |
March 31, 2017 |  | 309,796 |  |  | $ | 1.9 |
Summary of restricted shares activity | The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the three months ended March 31, 2017 and 2016:
|  | Three Months Ended March 31,
|  | 2017 |  | 2016
Millions, except share amounts |  | Restricted Shares |  | Unamortized Issue Date Fair Value |  | Restricted Shares |  | Unamortized Issue Date Fair Value
Non-vested, |  |  |  |  |  |  |  |  |  |  |  |
Beginning of period |  | 395,872 |  |  | $ | 2.1 |  |  | 382,722 |  |  | $ | 2.5 |
Issued |  | 461,160 |  |  | 7.4 |  |  | 170,650 |  |  | 2.3 |
Vested |  | (157,500 | ) |  | — |  |  | (157,500 | ) |  | — |
Forfeited |  | — |  |  | — |  |  | — |  |  | — |
Expense recognized |  | — |  |  | (.9 | ) |  | — |  |  | (.5 | )
End of period |  | 699,532 |  |  | $ | 8.6 |  |  | 395,872 |  |  | $ | 4.3 |

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- Definition Tabular disclosure of the number and weighted-average grant date fair value for outstanding performance shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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