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Commitments and Contingencies - Purchase Commitments (Details)
$ in Millions
Mar. 31, 2018
USD ($)
Other commitments  
Sales tax liability $ 0.1
Minimum  
Other commitments  
Sales tax liability 0.1
Maximum  
Other commitments  
Sales tax liability 3.7
Compression units  
Other commitments  
Future purchase commitments $ 128.7