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Equity Investments - Additional Information (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]      
Equity investment impairment loss [1] $ 3,110    
Western Gas Partners, LP [Member] | Fort Union [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity investment difference between carrying and underlying value     $ (3,100)
Equity investment ownership percentage     14.81%
Equity investment impairment loss 3,110 [1] $ 3,000  
Western Gas Partners, LP [Member] | Rendezvous [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity investment difference between carrying and underlying value     $ 34,300
Equity investment impairment loss [1] 0    
Western Gas Partners, LP [Member] | White Cliffs [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity investment difference between carrying and underlying value     $ (6,400)
Equity investment impairment loss [1] $ 0    
Western Gas Partners, LP [Member] | White Cliffs [Member] | Affiliates [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity investment ownership percentage     0.40%
Western Gas Partners, LP [Member] | Whitethorn [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity investment difference between carrying and underlying value     $ (39,100)
[1] Recorded in Impairments in the consolidated statements of operations.