Inventories, net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventories, net additional information
Inventory Write-down	$ 6.2	$ 6.2
Charges to cost of sales due to lower of cost or market value		8.1	$ 0.8	$ 0.5
Inventory on consignment at customer locations	3.6	3.6	3.4
Inventory reserves
Inventories, net additional information
Increase in inventory reserves		5.3
Inventory reserves	$ 14.2	$ 14.2	$ 8.8