Income Taxes - Tax Reform Impact (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Income Tax Provision
Reduction in U.S. Federal corporate rate	$ 7.0
One-time repatriation transition tax	7.7
Revision to deduction for executive compensation	0.8
Tax Act impact as of and for the year ended December 31, 2017	15.5
Income Taxes Payable
One-time repatriation transition tax	1.0
Deferred Tax Assets and Liabilities
Reduction in U.S. Federal corporate rate	7.0
Revision to deduction for executive compensation	(0.8)
Tax Act impact as of and for the year ended December 31, 2017	(7.8)
Other Long-term Liabilities
One-time repatriation transition tax	$ 6.7