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Goodwill and Other Intangible Assets (Goodwill and Intangible Assets) (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Aug. 04, 2016 | Dec. 31, 2015
Goodwill [Line Items] |  |  |  |
Goodwill | $ 25.9 | $ 25.9 |  | $ 18.6
Intangible assets, gross (excluding goodwill) | 71.0 | 43.5 |  |
Amortization of Intangible Assets | 34.8 | 24.2 |  |
Intangible assets, net (excluding goodwill) | 36.2 | 19.3 |  |
Intangible assets, gross (including goodwill) | 96.9 | 69.4 |  |
Goodwill and intangible assets | 62.1 | 45.2 |  |
MediaAlpha |  |  |  |
Goodwill [Line Items] |  |  |  |
Goodwill | 18.3 | 18.3 |  |
Intangible assets, gross (excluding goodwill) | 69.9 | 42.4 |  |
Amortization of Intangible Assets | 34.5 | 24.1 |  |
Intangible assets, net (excluding goodwill) | 35.4 | 18.3 |  |
Buzzmove |  |  |  |
Goodwill [Line Items] |  |  |  |
Goodwill | 7.6 | 7.6 | $ 7.6 |
Intangible assets, gross (excluding goodwill) | 1.1 | 1.1 |  |
Amortization of Intangible Assets | 0.3 | 0.1 |  |
Intangible assets, net (excluding goodwill) | $ 0.8 | 1.0 | $ 1.1 |
Customer relationships | MediaAlpha |  |  |  |
Goodwill [Line Items] |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 8 years |  |  |
Intangible assets, gross (excluding goodwill) | $ 36.6 | 10.0 |  |
Amortization of Intangible Assets | 10.2 | 6.2 |  |
Intangible assets, net (excluding goodwill) | $ 26.4 | 3.8 |  |
Information technology | MediaAlpha |  |  |  |
Goodwill [Line Items] |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 5 years |  |  |
Intangible assets, gross (excluding goodwill) | $ 33.3 | 32.4 |  |
Amortization of Intangible Assets | 24.3 | 17.9 |  |
Intangible assets, net (excluding goodwill) | $ 9.0 | 14.5 |  |
Information technology | Buzzmove |  |  |  |
Goodwill [Line Items] |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 5 years |  |  |
Intangible assets, gross (excluding goodwill) | $ 0.5 | 0.5 |  |
Amortization of Intangible Assets | 0.2 | 0.0 |  |
Intangible assets, net (excluding goodwill) | $ 0.3 | 0.5 |  |
Trademark | Buzzmove |  |  |  |
Goodwill [Line Items] |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 7 years |  |  |
Intangible assets, gross (excluding goodwill) | $ 0.6 | 0.6 |  |
Amortization of Intangible Assets | 0.1 | 0.1 |  |
Intangible assets, net (excluding goodwill) | 0.5 | 0.5 |  |
Other intangible assets |  |  |  |
Goodwill [Line Items] |  |  |  |
Intangible assets, net (excluding goodwill) | $ 36.2 | $ 19.3 |  | $ 26.9

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