Quarterly report pursuant to Section 13 or 15(d)

Acquisitions - WTL Oil Acquisition (Narrative) (Details)

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Acquisitions - WTL Oil Acquisition (Narrative) (Details) - USD ($)
$ in Thousands
1 Months Ended 3 Months Ended 6 Months Ended
May 31, 2018
Jul. 31, 2018
Jun. 30, 2018
Jun. 30, 2018
Jun. 30, 2017
Business Acquisition [Line Items]          
Cash paid to acquire a business       $ 13,356 $ 39,570
WTL Oil LLC          
Business Acquisition [Line Items]          
Purchase price $ 5,500        
Consideration receivable $ 600        
Acquisition related costs     $ 100    
Subsequent Event | WTL Oil LLC          
Business Acquisition [Line Items]          
Cash paid to acquire a business   $ 600