Summary of Significant Accounting Policies - Property and Depreciation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Property and Depreciation
Assets in which units-of-production method of depreciation is used	$ 68.8
Buildings
Property and Depreciation
Weighted average useful lives	18 years
Land improvements
Property and Depreciation
Weighted average useful lives	19 years
Machinery and equipment
Property and Depreciation
Weighted average useful lives	9 years