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Subsequent Event | 12 Months Ended
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Dec. 31, 2017
Subsequent Events [Abstract] |
Subsequent Events | Subsequent Events DavidShield On January 24, 2018, White Mountains acquired a 50% equity stake in DavidShield Life Insurance Agency (2000) Ltd. for approximately $28.0 million, its joint venture partner in PassportCard and a provider of expatriate medical and other accident and health insurance coverages. CrossHarbor On January 26, 2018, White Mountains entered into an agreement to invest up to $50.0 million in CrossHarbor Institutional Partners 2018, L.P. CrossHarbor Capital is an alternative investment management firm that invests in core-plus, value-add, and opportunistic commercial real estate transactions. Kudu On February 5, 2018, White Mountains entered into an agreement to invest up to $125.0 million in Kudu Investment Management, LLC (“Kudu”), a capital provider to asset management and wealth management firms. Through February of 2018, White Mountains has invested $1.8 million in Kudu.

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- Definition The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 855 -URI http://asc.fasb.org/topic&trid=2122774 + Details
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