Transactions with Related Persons	12 Months Ended
Dec. 31, 2015
Related Party Transactions [Abstract]
Transactions with Related Persons	Transactions with Related Persons Prospector Mr. John Gillespie, the founder and Managing Member of Prospector, retired from the WTM Board of Directors in May 2015. Until June 30, 2015, Prospector served 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. At that time, the investment management agreements between WM Advisors and Prospector and OneBeacon and Prospector and the Consulting Agreement described below were terminated. Pursuant to an investment management agreements with WM Advisors (the “WMA Agreement”) and OneBeacon (the “OneBeacon Agreement”), Prospector charged WM Advisors and OneBeacon fees based on the following schedule: 100 basis points on the first $200 million of assets under management; 50 basis points on the next $200 million; and 25 basis points on amounts over $400 million. As of December 31, 2014, Prospector managed $195.7 million of assets under the WMA Agreement and $431.2 million of assets under the OneBeacon Agreement, including $202.9 million of ERISA assets. During 2015, 2014 and 2013, Prospector earned $2.1 million, $6.5 million, and $6.5 million in total fees pursuant to the investment management agreements with WM Advisors and OneBeacon. Prospector also had a separate investment management agreement with Symetra that was terminated in the fourth quarter of 2015. Prospector also advised 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 2014-2016 cycle and 7,000 performance shares for the 2013-2015 cycle. Under the terms of the Consulting Agreement, Prospector earned a prorated portion of the outstanding performance share grants at the time of the termination of the Consulting Agreement and was paid $5.5 million in respect thereof. Pursuant to a pre-existing revenue sharing agreement (the “Revenue Agreement”), Prospector paid White Mountains 6% of the annual revenues in excess of $500,000 of certain of Prospector’s funds in return for White Mountains having made a founding investment in 1997. White Mountains and Prospector mutually agreed to terminate the Revenue Agreement as of June 30, 2015. During 2014 and 2013, White Mountains earned $0.4 million, and $0.9 million under the Revenue Agreement. No amount was earned under the Revenue Agreement in 2015. Prior to fully redeeming their interests on June 30, 2015, White Mountains and OneBeacon had interests in limited partnership investments managed by Prospector (the “Funds”). As of December 31, 2014, White Mountains had $82.4 million invested in these limited partnerships. This total included $15.8 million of OneBeacon assets. Under the limited partnership agreements, Prospector served as general partner and general manager of the Funds and was paid management and incentive performance fees by White Mountains and OneBeacon. For the years ended December 31, 2015, 2014 and 2013, White Mountains and OneBeacon incurred $0.4 million, $1.1 million and $1.3 million in management fees and $0.1 million, $0.7 million and $3.2 million in incentive fees. Oakum Bay Capital Mr. Kernan Oberting, a Managing Director of White Mountains Capital, 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. Mr. Oberting is a limited partner in KCP and TCF. 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. During 2012, White Mountains invested $9.5 million in the TCF hedge funds, which were redeemed in the fourth quarter of 2015 for $8.9 million. Other Relationships and Transactions WM Advisors provides investment advisory and management services to Symetra. As of December 31, 2015 and 2014, WMA had $22.1 billion and $30.9 billion of assets under management from Symetra. During 2015, 2014 and 2013, WMA earned $8.0 million, $18.4 million and $16.5 million in fees from Symetra. During 2015, the Company repurchased shares from Franklin Mutual Advisers, a beneficial owner of the Company, in two transactions. On June 1, 2015, the Company repurchased 19,688 WTM common shares for $650.03 per share, the market price at the time the agreement was reached. On September 17, 2015, the Company repurchased 26,300 WTM common shares for $761.50, the market price at the time the agreement was reached.

Transactions with Related Persons

Prospector

Mr. John Gillespie, the founder and Managing Member of Prospector, retired from the WTM Board of Directors in May 2015. Until June 30, 2015, Prospector served 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. At that time, the investment management agreements between WM Advisors and Prospector and OneBeacon and Prospector and the Consulting Agreement described below were terminated.

Pursuant to an investment management agreements with WM Advisors (the “WMA Agreement”) and OneBeacon (the “OneBeacon Agreement”), Prospector charged WM Advisors and OneBeacon fees based on the following schedule: 100 basis points on the first $200 million of assets under management; 50 basis points on the next $200 million; and 25 basis points on amounts over $400 million. As of December 31, 2014, Prospector managed $195.7 million of assets under the WMA Agreement and $431.2 million of assets under the OneBeacon Agreement, including $202.9 million of ERISA assets. During 2015, 2014 and 2013, Prospector earned $2.1 million, $6.5 million, and $6.5 million in total fees pursuant to the investment management agreements with WM Advisors and OneBeacon. Prospector also had a separate investment management agreement with Symetra that was terminated in the fourth quarter of 2015.

Prospector also advised 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 2014-2016 cycle and 7,000 performance shares for the 2013-2015 cycle. Under the terms of the Consulting Agreement, Prospector earned a prorated portion of the outstanding performance share grants at the time of the termination of the Consulting Agreement and was paid $5.5 million in respect thereof.

Pursuant to a pre-existing revenue sharing agreement (the “Revenue Agreement”), Prospector paid White Mountains 6% of the annual revenues in excess of $500,000 of certain of Prospector’s funds in return for White Mountains having made a founding investment in 1997. White Mountains and Prospector mutually agreed to terminate the Revenue Agreement as of June 30, 2015. During 2014 and 2013, White Mountains earned $0.4 million, and $0.9 million under the Revenue Agreement. No amount was earned under the Revenue Agreement in 2015.

Prior to fully redeeming their interests on June 30, 2015, White Mountains and OneBeacon had interests in limited partnership investments managed by Prospector (the “Funds”). As of December 31, 2014, White Mountains had $82.4 million invested in these limited partnerships. This total included $15.8 million of OneBeacon assets. Under the limited partnership agreements, Prospector served as general partner and general manager of the Funds and was paid management and incentive performance fees by White Mountains and OneBeacon. For the years ended December 31, 2015, 2014 and 2013, White Mountains and OneBeacon incurred $0.4 million, $1.1 million and $1.3 million in management fees and $0.1 million, $0.7 million and $3.2 million in incentive fees.

Oakum Bay Capital

Mr. Kernan Oberting, a Managing Director of White Mountains Capital, 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. Mr. Oberting is a limited partner in KCP and TCF.

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.

During 2012, White Mountains invested $9.5 million in the TCF hedge funds, which were redeemed in the fourth quarter of 2015 for $8.9 million.

Other Relationships and Transactions

WM Advisors provides investment advisory and management services to Symetra. As of December 31, 2015 and 2014, WMA had $22.1 billion and $30.9 billion of assets under management from Symetra. During 2015, 2014 and 2013, WMA earned $8.0 million, $18.4 million and $16.5 million in fees from Symetra.

During 2015, the Company repurchased shares from Franklin Mutual Advisers, a beneficial owner of the Company, in two transactions. On June 1, 2015, the Company repurchased 19,688 WTM common shares for $650.03 per share, the market price at the time the agreement was reached. On September 17, 2015, the Company repurchased 26,300 WTM common shares for $761.50, the market price at the time the agreement was reached.