Revenue Recognition - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Selling General and Administrative Expenses [Member]
Disaggregation Of Revenue [Line Items]
Costs for shipments to customers	$ 2.7	$ 2.3
Cost of Sales [Member]
Disaggregation Of Revenue [Line Items]
Costs for shipments to customers	$ 1.3	$ 1.5