Quarterly report pursuant to Section 13 or 15(d)

Trade Inventory (Narrative) (Details)

v3.8.0.1
Trade Inventory (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Trade Inventory [Abstract]    
Inventory writedowns included in costs of goods sold $ 0.0 $ 0.4