Financial Instruments and Derivative Financial Instruments - Concentration of Credit Risks (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financial Instruments and Derivative Financial Instruments
Sales	$ 290.1	$ 272.2	$ 277.9	$ 244.1	$ 269.4	$ 202.7	$ 199.8	$ 171.0	$ 1,084.3	$ 842.9	$ 722.0
Geographic Concentration Risk | Sales | Foreign
Financial Instruments and Derivative Financial Instruments
Concentration risk (percent)									44.00%	44.00%	48.00%
Customer Concentration Risk | Sales | Praxair and Linde
Financial Instruments and Derivative Financial Instruments
Concentration risk (percent)									11.20%
Sales									$ 121.6
Customer Concentration Risk | Sales | Air Gas and Air Liquide
Financial Instruments and Derivative Financial Instruments
Concentration risk (percent)											12.50%
Sales											$ 90.6
Customer Concentration Risk | Sales | Ten Largest Customers
Financial Instruments and Derivative Financial Instruments
Concentration risk (percent)									39.00%	38.00%	41.00%