Supplemental Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018
Long Lived Assets Held-for-sale [Line Items]
Gain from antitrust litigation settlement	$ 0			$ (3,591)
Gain (loss) on disposition of assets	383	$ 0	$ (942)
Arizona
Long Lived Assets Held-for-sale [Line Items]
Gain (loss) on disposition of assets	$ 400
Belgium
Long Lived Assets Held-for-sale [Line Items]
Gain (loss) on disposition of assets			$ 942