Income Taxes - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Effective income tax rate (percent)		32.10%	6.10%
Effective income tax rate reconciliation, increase (decrease) to the tax provision		$ 5,700,000
Impairment loss		0	$ 358,200,000
Gross unrecognized tax benefit	$ 5,900,000	8,300,000
Expected change in unrecognized tax benefits		5,100,000
Accrued interest on income taxes	1,100,000	1,600,000
Accrued penalties on income taxes, less than	100,000	$ 100,000
Tax Cuts and Jobs Act of 2017, incomplete accounting, provisional income tax expense (benefit)	$ (77,500,000)