Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 110,630	$ 100,008	$ 329,319	$ 305,790
United States
Disaggregation of Revenue [Line Items]
Revenues	95,288		284,351
Asia
Disaggregation of Revenue [Line Items]
Revenues	1,928		6,789
Canada
Disaggregation of Revenue [Line Items]
Revenues	2,564		9,353
Europe
Disaggregation of Revenue [Line Items]
Revenues	4,457		14,605
Mexico
Disaggregation of Revenue [Line Items]
Revenues	1,031		2,137
Middle East
Disaggregation of Revenue [Line Items]
Revenues	4,602		9,958
Other
Disaggregation of Revenue [Line Items]
Revenues	760		2,126
Revenue recognized over time
Disaggregation of Revenue [Line Items]
Revenues	3,455		9,203
Revenue recognized at a point in time
Disaggregation of Revenue [Line Items]
Revenues	$ 107,175		$ 320,116