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Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2019 | Jun. 30, 2019 | Dec. 31, 2018 | Jun. 30, 2018 | Dec. 31, 2017
Goodwill [Line Items] |  |  |  |  |
Goodwill, acquisition date fair value | $ 424.8 |  | $ 379.9 |  |
Goodwill | 424.8 | $ 428.6 | 379.9 | $ 25.9 | $ 25.9
Other intangible assets, accumulated amortization | 22.5 |  | 53.6 |  |
Goodwill and intangible assets, acquisition date fair value | 683.4 |  | 591.1 |  |
Goodwill and intangible assets, net carrying value | 660.9 |  | 537.5 |  |
NSM Holding Co LLC |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Goodwill, acquisition date fair value | 397.0 |  | 354.3 |  |
Goodwill | 397.0 |  | 354.3 |  |
Other intangible assets, acquisition date fair value | 255.4 |  | 140.2 |  |
Other intangible assets, accumulated amortization | 21.8 |  | 8.3 |  |
Other intangible assets, net carrying value | 233.6 |  | 131.9 |  |
Kudu investments |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Goodwill, acquisition date fair value | 7.6 |  | 0.0 |  |
Goodwill | 7.6 |  | 0.0 |  |
MediaAlpha |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Goodwill, acquisition date fair value | 0.0 |  | 18.3 |  |
Goodwill | 0.0 |  | 18.3 |  |
Other intangible assets, acquisition date fair value | 0.0 |  | 69.9 |  |
Other intangible assets, accumulated amortization | 0.0 |  | 44.8 |  |
Other intangible assets, net carrying value | 0.0 |  | 25.1 |  |
Other Operations |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Goodwill, acquisition date fair value | 20.2 |  | 7.3 |  |
Goodwill | 20.2 |  | 7.3 |  |
Other intangible assets, acquisition date fair value | 1.0 |  | 1.1 |  |
Other intangible assets, accumulated amortization | 0.5 |  | 0.5 |  |
Other intangible assets, net carrying value | 0.5 |  | 0.6 |  |
Customer relationships | NSM Holding Co LLC |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | 110.5 |  | 85.3 |  |
Other intangible assets, accumulated amortization | 15.5 |  | 6.0 |  |
Other intangible assets, net carrying value | $ 95.0 |  | 79.3 |  |
Acquired finite-lived intangible assets, weighted average useful life | 9 years |  |  |  |
Customer relationships | MediaAlpha |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 0.0 |  | 26.8 |  |
Other intangible assets, accumulated amortization | 0.0 |  | 4.9 |  |
Other intangible assets, net carrying value | $ 0.0 |  | 21.9 |  |
Acquired finite-lived intangible assets, weighted average useful life | 9 years |  |  |  |
Trade names | NSM Holding Co LLC |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 57.1 |  | 51.2 |  |
Other intangible assets, accumulated amortization | 4.2 |  | 1.8 |  |
Other intangible assets, net carrying value | $ 52.9 |  | 49.4 |  |
Acquired finite-lived intangible assets, weighted average useful life | 19 years |  |  |  |
Trade names | Kudu investments |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 2.2 |  | 0.0 |  |
Other intangible assets, accumulated amortization | 0.2 |  | 0.0 |  |
Other intangible assets, net carrying value | $ 2.0 |  | 0.0 |  |
Acquired finite-lived intangible assets, weighted average useful life | 7 years |  |  |  |
Trade names | Other Operations |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 0.6 |  | 0.6 |  |
Other intangible assets, accumulated amortization | 0.2 |  | 0.2 |  |
Other intangible assets, net carrying value | $ 0.4 |  | 0.4 |  |
Acquired finite-lived intangible assets, weighted average useful life | 7 years |  |  |  |
Information technology | NSM Holding Co LLC |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 3.6 |  | 3.7 |  |
Other intangible assets, accumulated amortization | 1.1 |  | 0.5 |  |
Other intangible assets, net carrying value | $ 2.5 |  | 3.2 |  |
Acquired finite-lived intangible assets, weighted average useful life | 5 years |  |  |  |
Information technology | MediaAlpha |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 0.0 |  | 33.3 |  |
Other intangible assets, accumulated amortization | 0.0 |  | 30.9 |  |
Other intangible assets, net carrying value | $ 0.0 |  | 2.4 |  |
Acquired finite-lived intangible assets, weighted average useful life | 5 years |  |  |  |
Information technology | Other Operations |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 0.4 |  | 0.5 |  |
Other intangible assets, accumulated amortization | 0.3 |  | 0.3 |  |
Other intangible assets, net carrying value | $ 0.1 |  | 0.2 |  |
Acquired finite-lived intangible assets, weighted average useful life | 5 years |  |  |  |
Other Operations | NSM Holding Co LLC |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 1.7 |  |  |  |
Other intangible assets, accumulated amortization | 0.7 |  |  |  |
Other intangible assets, net carrying value | $ 1.0 |  |  |  |
Acquired finite-lived intangible assets, weighted average useful life | 3 years |  |  |  |
Other Operations | MediaAlpha |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 0.0 |  | 9.8 |  |
Other intangible assets, accumulated amortization | 0.0 |  | 9.0 |  |
Other intangible assets, net carrying value | $ 0.0 |  | 0.8 |  |
Acquired finite-lived intangible assets, weighted average useful life | 3 years |  |  |  |
Renewal Rights | NSM Holding Co LLC |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 82.5 |  |  |  |
Other intangible assets, accumulated amortization | 0.3 |  |  |  |
Other intangible assets, net carrying value | $ 82.2 |  |  |  |
Acquired finite-lived intangible assets, weighted average useful life | 12 years |  |  |  |
Other Intangible Assets |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Other intangible assets, acquisition date fair value | $ 258.6 |  | 211.2 |  |
Other intangible assets, accumulated amortization | 22.5 |  | 53.6 |  |
Other intangible assets, net carrying value | 236.1 |  | 157.6 |  |
Non-controlling interest |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Goodwill and intangible assets, net carrying value | (25.0) |  | (40.6) |  |
Total |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |
Goodwill and intangible assets, net carrying value | $ 635.9 |  | $ 496.9 |  |

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