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Accounts Receivable from Customers (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Accounts Receivable [Line Items]    
Accounts Receivable $ 145,299 $ 167,536
Oil, gas, and NGL production revenue [Member]    
Accounts Receivable [Line Items]    
Accounts Receivable $ 109,400 $ 107,200