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Summary of Significant Accounting Policies (Basis of Presentation) (Details) $ / shares in Units, $ in Millions | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2017 USD ($) publisher advertiser | Sep. 30, 2016 USD ($) | Sep. 28, 2017 $ / shares | Jun. 30, 2017 | Dec. 31, 2016 | Jul. 31, 2012 USD ($)
HG Global |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Percentage of par value of policy reinsured | 15.00% |  |  |  |  |
Surplus notes |  |  |  |  |  | $ 503.0
MediaAlpha |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Number of advertisers | advertiser | 330 |  |  |  |  |
Number of publishers | publisher | 280 |  |  |  |  |
Preferred Stock | HG Global |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Ownership interest (as a percent) | 96.90% |  |  | 96.90% | 96.90% |
Common Stock | HG Global |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Ownership interest (as a percent) | 88.40% |  |  | 88.40% | 88.40% |
Restricted Stock |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Payments related to tax withholding for share-based compensation | $ 9.3 | $ 5.8 |  |  |  |
OneBeacon |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Business acquisition, share price | $ / shares |  |  | $ 18.10 |  |  |

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