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Income Taxes - Narrative (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Apr. 30, 2018 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Investments, Owned, Federal Income Tax Note [Line Items] |  |  |  |  |  |
Income tax (provision) benefit |  | $ (6,900,000) | $ 1,900,000 | $ (16,800,000) | $ 2,000,000 |
Transition tax expense |  |  |  | 5,900,000 |  | $ 0
Discrete tax benefit related to amending tax returns for prior periods |  |  |  | 5,800,000 |  |
Federal taxable income on the mandatory deemed repatriation of foreign E&P |  |  |  | 97,500,000 |  | 100,000,000
Transition tax liability |  | $ 34,100,000 |  | 34,100,000 |  | $ 35,000,000
Adjustment to transition tax liability |  |  |  | $ 5,900,000 |  |
Payment of transition tax liability | $ 500,000 |  |  |  |  |
Effective income tax rate |  | 11.00% |  | 8.10% |  |
Discrete tax benefits (expense) |  | $ (900,000) | $ 300,000 | $ (900,000.0) | $ 7,000,000 |
Tax Cuts and Jobs Act, Transition Tax Liability [Member] |  |  |  |  |  |
Investments, Owned, Federal Income Tax Note [Line Items] |  |  |  |  |  |
Tax credit carryforward utilized |  | 28,200,000 |  | 28,200,000 |  |
Federal | Tax Cuts and Jobs Act, Transition Tax Liability [Member] |  |  |  |  |  |
Investments, Owned, Federal Income Tax Note [Line Items] |  |  |  |  |  |
NOL tax attributes preserved |  | $ 97,500,000 |  | $ 97,500,000 |  |

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