Transactions with Related Persons	12 Months Ended
Dec. 31, 2014
Related Party Transactions [Abstract]
Transactions with Related Persons	Transactions with Related Persons Prospector Mr. John Gillespie, a director of White Mountains, is the founder and Managing Member of Prospector. Prospector serves as a discretionary adviser with respect to specified assets, primarily common equity securities and convertible fixed maturity investments, managed directly or through WM Advisors on behalf of White Mountains and other clients of WM Advisors. Pursuant to an investment management agreement with WM Advisors (the “WMA Agreement”), Prospector charges WM Advisors fees based on the following schedule: 100 basis points on the first $200.0 million of assets under management; 50 basis points on the next $200.0 million and 25 basis points on amounts over $400.0 million. As of December 31, 2014, Prospector managed a total of $195.7 million of assets for White Mountains (excluding OneBeacon and Symetra) under this arrangement. Prospector has a separate investment management agreement with Symetra that began on July 1, 2010. Until that date, Symetra was a party to the WMA Agreement and subject to the above fee schedule. Prospector has separate investment management agreements with OneBeacon (the “OneBeacon Agreements”) pursuant to which Prospector supervises and directs specified assets, primarily common equity securities and convertible fixed maturity investments, including assets in OneBeacon’s defined benefit and defined contribution plans (the “ERISA Assets”). All assets managed under the OneBeacon Agreements are subject to a single fee schedule that is substantially similar to the terms of the WMA Agreement fee schedule. As of December 31, 2014, Prospector managed $431.2 million of assets for OneBeacon under this arrangement, including $202.9 million of ERISA Assets. During 2014, 2013 and 2012, Prospector earned $6.5 million, $6.5 million, and $6.4 million in total fees pursuant to the WMA Agreement and the OneBeacon Agreements. Prospector also advises White Mountains on matters including capital management, asset allocation, private equity investments and mergers and acquisitions. Pursuant to a Consulting Agreement for those services, Prospector was granted 6,250 performance shares for the 2015-2017 cycle, 6,250 performance shares for the 2014-2016 cycle and 7,000 performance shares for the 2013-2015 cycle. In accordance with the terms of the WTM Incentive Plan, performance against target governing the performance shares will be confirmed by the Compensation Committee of the Board following the end of each performance cycle and the number of performance shares actually awarded at that time will range from 0% to 200% of the target number granted. Based on the Company’s performance, Prospector received 145.5% of the 7,750 performance shares granted for the 2012-2014 performance cycle for a total payout of $7.5 million. Unless and until the Consulting Agreement has been terminated, and subject to the approval of the Compensation Committee, at the beginning of each performance cycle Prospector is to be granted performance shares with a value of approximately $4.5 million. The Compensation Committee establishes the performance target for such performance shares. Pursuant to a revenue sharing agreement, Prospector has agreed to pay White Mountains 6% of the revenues in excess of $500,000 of certain of Prospector’s funds in return for White Mountains having made a founding investment in 1997. During 2014, 2013 and 2012, White Mountains earned $0.4 million, $0.9 million, and $0.5 million under this arrangement. As of December 31, 2014, White Mountains had $82.4 million invested in limited partnership investment interests managed by Prospector (the “Funds”). This total includes $15.8 million of OneBeacon assets. Under the limited partnership agreements, Prospector serves as general partner and general manager of the Funds and is paid management and incentive performance fees by White Mountains and OneBeacon. For the years ended December 31, 2014, 2013 and 2012, White Mountains and OneBeacon incurred $1.1 million, $1.3 million and $1.1 million in management fees and $0.7 million, $3.2 million and $1.3 million in incentive fees. Oakum Bay Capital Mr. Kernan Oberting, a Managing Director of White Mountains Capital and President of Sirius Capital Markets, founded Oakum Bay Capital (“OBC”). OBC serves as the general manager and owns general partnership interests in KVO Capital Partners (“KCP”) and the Trimarc Capital Fund (“TCF”) hedge funds. In connection with Mr. Oberting commencing employment with White Mountains Capital, on July 16, 2012, White Mountains purchased $2.0 million of preferred stock and received 7.5% of the common equity of OBC. After giving effect to the White Mountains’s investment, Mr. Oberting and his family beneficially owned 67.5% of the common equity of OBC. During 2013, Mr. Oberting and his family assigned all of their common equity interests to unaffiliated OBC management with effect from January 1, 2013. In September 2013, White Mountains exchanged its preferred stock and common equity interest in OBC for $500,000 in cash and a portion of OBC’s revenue for the next ten years. As of December 31, 2014, White Mountains investment in TCF was $7.8 million. Mr. Oberting is a limited partner in KCP and TCF. Mr. Barrette had a limited partnership investment in KCP that was redeemed in full in September 2012. For the year ended December 31, 2013, White Mountains paid investment management fees $0.1 million to OBC. Other Relationships and Transactions WM Advisors provides investment advisory and management services to Symetra. As of December 31, 2014 and 2013, WMA had $30.9 billion and $27.8 billion of assets under management from Symetra. During 2014, 2013 and 2012, WMA earned $18.4 million, $16.5 million and $15.9 million in fees from Symetra. On March 15, 2013, the Company repurchased 140,000 WTM common shares from the estate of John J. Byrne, a beneficial owner of the Company. The price per share was $563.57, the market price at the time the agreement was reached.

Transactions with Related Persons

Prospector

Mr. John Gillespie, a director of White Mountains, is the founder and Managing Member of Prospector. Prospector serves as a discretionary adviser with respect to specified assets, primarily common equity securities and convertible fixed maturity investments, managed directly or through WM Advisors on behalf of White Mountains and other clients of WM Advisors.

Pursuant to an investment management agreement with WM Advisors (the “WMA Agreement”), Prospector charges WM Advisors fees based on the following schedule: 100 basis points on the first $200.0 million of assets under management; 50 basis points on the next $200.0 million and 25 basis points on amounts over $400.0 million. As of December 31, 2014, Prospector managed a total of $195.7 million of assets for White Mountains (excluding OneBeacon and Symetra) under this arrangement. Prospector has a separate investment management agreement with Symetra that began on July 1, 2010. Until that date, Symetra was a party to the WMA Agreement and subject to the above fee schedule.

Prospector has separate investment management agreements with OneBeacon (the “OneBeacon Agreements”) pursuant to which Prospector supervises and directs specified assets, primarily common equity securities and convertible fixed maturity investments, including assets in OneBeacon’s defined benefit and defined contribution plans (the “ERISA Assets”). All assets managed under the OneBeacon Agreements are subject to a single fee schedule that is substantially similar to the terms of the WMA Agreement fee schedule. As of December 31, 2014, Prospector managed $431.2 million of assets for OneBeacon under this arrangement, including $202.9 million of ERISA Assets.

During 2014, 2013 and 2012, Prospector earned $6.5 million, $6.5 million, and $6.4 million in total fees pursuant to the WMA Agreement and the OneBeacon Agreements.

Prospector also advises White Mountains on matters including capital management, asset allocation, private equity investments and mergers and acquisitions. Pursuant to a Consulting Agreement for those services, Prospector was granted 6,250 performance shares for the 2015-2017 cycle, 6,250 performance shares for the 2014-2016 cycle and 7,000 performance shares for the 2013-2015 cycle. In accordance with the terms of the WTM Incentive Plan, performance against target governing the performance shares will be confirmed by the Compensation Committee of the Board following the end of each performance cycle and the number of performance shares actually awarded at that time will range from 0% to 200% of the target number granted. Based on the Company’s performance, Prospector received 145.5% of the 7,750 performance shares granted for the 2012-2014 performance cycle for a total payout of $7.5 million. Unless and until the Consulting Agreement has been terminated, and subject to the approval of the Compensation Committee, at the beginning of each performance cycle Prospector is to be granted performance shares with a value of approximately $4.5 million. The Compensation Committee establishes the performance target for such performance shares.

Pursuant to a revenue sharing agreement, Prospector has agreed to pay White Mountains 6% of the revenues in excess of $500,000 of certain of Prospector’s funds in return for White Mountains having made a founding investment in 1997. During 2014, 2013 and 2012, White Mountains earned $0.4 million, $0.9 million, and $0.5 million under this arrangement.

As of December 31, 2014, White Mountains had $82.4 million invested in limited partnership investment interests managed by Prospector (the “Funds”). This total includes $15.8 million of OneBeacon assets. Under the limited partnership agreements, Prospector serves as general partner and general manager of the Funds and is paid management and incentive performance fees by White Mountains and OneBeacon. For the years ended December 31, 2014, 2013 and 2012, White Mountains and OneBeacon incurred $1.1 million, $1.3 million and $1.1 million in management fees and $0.7 million, $3.2 million and $1.3 million in incentive fees.

Oakum Bay Capital

Mr. Kernan Oberting, a Managing Director of White Mountains Capital and President of Sirius Capital Markets, founded Oakum Bay Capital (“OBC”). OBC serves as the general manager and owns general partnership interests in KVO Capital Partners (“KCP”) and the Trimarc Capital Fund (“TCF”) hedge funds.

In connection with Mr. Oberting commencing employment with White Mountains Capital, on July 16, 2012, White Mountains purchased $2.0 million of preferred stock and received 7.5% of the common equity of OBC. After giving effect to the White Mountains’s investment, Mr. Oberting and his family beneficially owned 67.5% of the common equity of OBC. During 2013, Mr. Oberting and his family assigned all of their common equity interests to unaffiliated OBC management with effect from January 1, 2013.

In September 2013, White Mountains exchanged its preferred stock and common equity interest in OBC for $500,000 in cash and a portion of OBC’s revenue for the next ten years.

As of December 31, 2014, White Mountains investment in TCF was $7.8 million. Mr. Oberting is a limited partner in KCP and TCF. Mr. Barrette had a limited partnership investment in KCP that was redeemed in full in September 2012.

For the year ended December 31, 2013, White Mountains paid investment management fees $0.1 million to OBC.

Other Relationships and Transactions

WM Advisors provides investment advisory and management services to Symetra. As of December 31, 2014 and 2013, WMA had $30.9 billion and $27.8 billion of assets under management from Symetra. During 2014, 2013 and 2012, WMA earned $18.4 million, $16.5 million and $15.9 million in fees from Symetra.

On March 15, 2013, the Company repurchased 140,000 WTM common shares from the estate of John J. Byrne, a beneficial owner of the Company. The price per share was $563.57, the market price at the time the agreement was reached.