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Intangible Assets - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Goodwill [Line Items] |  |  |  |
Amortization expense | $ 25,900 | $ 8,700 | $ 5,200 |
Goodwill | 1,432,787 | 1,386,853 | 191,371 | $ 191,307
Non-Strategic |  |  |  |
Goodwill [Line Items] |  |  |  |
Gross goodwill | 200,000 |  |  |
Accumulated impairments | 114,100 |  |  |
Accumulated divestiture related write-offs | 85,900 |  |  |
Goodwill | $ 0 | $ 0 | $ 0 |

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