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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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