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Goodwill and Other Intangible Assets (Summary of Goodwill and Intangible Assets) (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | --- | ---
Goodwill [Line Items] |  |  |
Goodwill | $ 25.9 | $ 25.9 | $ 18.6
Intangible assets, net (excluding goodwill) | 36.2 | 19.3 |
Goodwill and intangible assets | 62.1 | 45.2 |
MediaAlpha |  |  |
Goodwill [Line Items] |  |  |
Goodwill | 18.3 | 18.3 |
Buzzmove |  |  |
Goodwill [Line Items] |  |  |
Goodwill | 7.6 | 7.6 |
Other intangible assets |  |  |
Goodwill [Line Items] |  |  |
Intangible assets, net (excluding goodwill) | 36.2 | 19.3 | $ 26.9
Other intangible assets | MediaAlpha |  |  |
Goodwill [Line Items] |  |  |
Intangible assets, net (excluding goodwill) | 35.4 | 18.3 |
Other intangible assets | Buzzmove |  |  |
Goodwill [Line Items] |  |  |
Intangible assets, net (excluding goodwill) | 0.8 | 1.0 |
Discontinued Operations, Held-for-sale |  |  |
Goodwill [Line Items] |  |  |
Goodwill and intangible assets | 0.0 | 1.2 |
Non-controlling interests |  |  |
Goodwill [Line Items] |  |  |
Goodwill and intangible assets | (21.1) | (17.1) |
Parent |  |  |
Goodwill [Line Items] |  |  |
Goodwill and intangible assets | $ 41.0 | $ 29.3 |

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 + Details
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- Definition Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16212-109274 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph ((a)(1),(b)) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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- Definition Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance. + References No definition available. + Details
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