Business Segment, Geographic and Major Customer Information - Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 70,989	$ 79,458	$ 190,591	$ 244,589
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	45,269	66,638	137,915	203,123
Other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	25,720	$ 12,820	$ 52,676	$ 41,466
Saudi Arabia
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 13,200
Sales | Geographic Concentration Risk | Saudi Arabia
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of revenue by major customers	18.60%