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Business Segments - Customer Concentration (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Customer concentration    
Revenue, Topic 606 $ 33,872 $ 55,072
Government    
Customer concentration    
Revenue, Topic 606 8,310 5,854
Permian Basin    
Customer concentration    
Revenue, Topic 606 23,202 43,286
TCPL Keystone    
Customer concentration    
Revenue, Topic 606 $ 1,471 $ 1,134