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Transactions with Affiliates - LTIP Award Activity Tables (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Related Party Transaction [Line Items]      
Value per unit of phantom units outstanding at beginning of year $ 43.39 $ 39.78 $ 47.20
Value per unit of phantom units vested during the period 43.39 39.78 47.20
Value per unit of phantom units granted during the period 35.08 43.39 39.78
Value per unit of phantom units outstanding at end of year $ 35.08 $ 43.39 $ 39.78
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Phantom units outstanding at beginning of year 5,763 5,658 12,537
Phantom units vested (5,763) (5,658) (12,537)
Phantom units granted 7,128 5,763 5,658
Phantom units outstanding at end of year 7,128 5,763 5,658
Western Gas Partners, LP [Member]      
Related Party Transaction [Line Items]      
Value per unit of phantom units outstanding at beginning of year $ 55.73 $ 49.30 $ 68.78
Value per unit of phantom units vested during the period 55.73 49.30 68.78
Value per unit of phantom units granted during the period 49.88 55.73 49.30
Value per unit of phantom units outstanding at end of year $ 49.88 $ 55.73 $ 49.30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Phantom units outstanding at beginning of year 7,180 7,304 5,477
Phantom units vested (7,180) (7,304) (5,477)
Phantom units granted 8,020 7,180 7,304
Phantom units outstanding at end of year 8,020 7,180 7,304