Income Taxes - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Investments, Owned, Federal Income Tax Note [Line Items]
Income tax (provision) benefit		$ (4,900,000)	$ 2,100,000	$ (9,900,000)	$ 100,000
Transition tax expense		(5,900,000)				$ 0
Discrete tax benefit related to amending tax returns for prior periods		5,900,000
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		6.10%		6.80%
Discrete tax benefits (expense)			$ 5,400,000	$ 0	$ 6,700,000
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