Inventories - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Inventory Disclosure [Abstract]
Lower of cost or market reserve adjustment for inventory	$ 1.5	$ 0.2	$ 2.4	$ 0.7