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Debt and Interest Expense - Additional Information (Details) - USD ($)
12 Months Ended
Feb. 15, 2019
Dec. 19, 2018
Feb. 16, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Mar. 31, 2019
Aug. 31, 2018
Mar. 31, 2018
Jun. 30, 2017
Feb. 25, 2014
Debt Instrument [Line Items]                      
APCWH Note Payable [1],[2]       $ 427,493,000 $ 98,966,000            
Long-term debt [1]       4,787,381,000 3,492,712,000            
Gain (loss) on interest-rate swaps [1]       $ (7,972,000) $ 0 $ 0          
Revolving Credit Facility [Member] | WGP RCF [Member]                      
Debt Instrument [Line Items]                      
Facility, maximum borrowing capacity     $ 35,000,000.0                
Facility, expiration date   Jun. 14, 2019                  
Facility, fee rate       0.30% 0.30%            
Facility, outstanding borrowings       $ 28,000,000              
Facility, available borrowing capacity       $ 7,000,000              
Facility, interest rate at period end       4.53% 3.57%            
Long-term debt         $ 28,000,000            
Revolving Credit Facility [Member] | WGP RCF [Member] | Minimum [Member]                      
Debt Instrument [Line Items]                      
Facility, fee rate       0.30%              
Revolving Credit Facility [Member] | WGP RCF [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Facility, fee rate       0.50%              
Revolving Credit Facility [Member] | WGP RCF [Member] | London Interbank Offered Rate (LIBOR) [Member]                      
Debt Instrument [Line Items]                      
Facility, variable rate floor       0.00%              
Revolving Credit Facility [Member] | WGP RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       2.00%              
Revolving Credit Facility [Member] | WGP RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       2.75%              
Revolving Credit Facility [Member] | WGP RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       1.00%              
Revolving Credit Facility [Member] | WGP RCF [Member] | Percentage Above Federal Funds Effective Rate [Member] | Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       0.50%              
Revolving Credit Facility [Member] | WGP RCF [Member] | Base Rate [Member] | Minimum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       1.00%              
Revolving Credit Facility [Member] | WGP RCF [Member] | Base Rate [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       1.75%              
Western Gas Partners, LP [Member] | Interest-Rate Swap [Member]                      
Debt Instrument [Line Items]                      
Gain (loss) on interest-rate swaps       $ (7,972,000)              
Western Gas Partners, LP [Member] | Interest-Rate Swap [Member] | Not Designated as Hedging Instrument [Member]                      
Debt Instrument [Line Items]                      
Interest-rate swap, collateral posted if credit risk related provision triggered       2,700,000              
Interest-rate swap, aggregate fair value of swaps with credit risk related features for which a net liability position existed       5,700,000              
Western Gas Partners, LP [Member] | Interest-Rate Swap [Member] | Not Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]                      
Debt Instrument [Line Items]                      
Interest-rate swap, liability fair value       $ 8,000,000              
Western Gas Partners, LP [Member] | 4.750% Senior Notes due 2028 [Member] | Senior Notes [Member]                      
Debt Instrument [Line Items]                      
Interest rate       4.75%              
Senior note, offering percent               99.818%      
Senior note, effective interest rate               4.885%      
Long-term debt       $ 395,841,000 0            
Western Gas Partners, LP [Member] | 5.500% Senior Notes due 2048 [Member] | Senior Notes [Member]                      
Debt Instrument [Line Items]                      
Interest rate       5.50%              
Senior note, offering percent               98.912%      
Senior note, effective interest rate               5.652%      
Long-term debt       $ 342,328,000 0            
Western Gas Partners, LP [Member] | 4.500% Senior Notes due 2028 [Member] | Senior Notes [Member]                      
Debt Instrument [Line Items]                      
Interest rate       4.50%              
Senior note, offering percent                 99.435%    
Senior note, effective interest rate                 4.682%    
Long-term debt       $ 394,631,000 0            
Western Gas Partners, LP [Member] | 5.300% Senior Notes due 2048 [Member] | Senior Notes [Member]                      
Debt Instrument [Line Items]                      
Interest rate       5.30%              
Senior note, offering percent                 99.169%    
Senior note, effective interest rate                 5.431%    
Long-term debt       $ 686,648,000 $ 0            
Western Gas Partners, LP [Member] | APCWH Note Payable [Member]                      
Debt Instrument [Line Items]                      
Interest rate       3.04% 2.09%            
Long-term debt       $ 427,493,000 $ 98,966,000            
Western Gas Partners, LP [Member] | APCWH Note Payable [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
APCWH Note Payable                   $ 500,000,000  
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member]                      
Debt Instrument [Line Items]                      
Facility, maximum borrowing capacity     $ 1,500,000,000.0               $ 1,200,000,000.0
Facility, expiration date     Feb. 15, 2023                
Facility, fee rate       0.20% 0.20%            
Facility, outstanding borrowings       $ 220,000,000              
Facility, available borrowing capacity       $ 1,300,000,000              
Facility, interest rate at period end       3.74% 2.87%            
Facility, expandable maximum borrowing capacity     $ 2,000,000,000                
Facility, outstanding letters of credit       $ 4,600,000              
Long-term debt       $ 220,000,000 $ 370,000,000            
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | Subsequent Event [Member]                      
Debt Instrument [Line Items]                      
Facility, expiration date Feb. 15, 2024                    
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | Scenario, Forecast [Member]                      
Debt Instrument [Line Items]                      
Facility, maximum borrowing capacity             $ 2,000,000,000.0        
Facility, accordion feature amount             $ 500,000,000.0        
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | Minimum [Member]                      
Debt Instrument [Line Items]                      
Facility, fee rate       0.125%              
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Facility, fee rate       0.25%              
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       1.00%              
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       1.50%              
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       1.00%              
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | Percentage Above Federal Funds Effective Rate [Member] | Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       0.50%              
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | Base Rate [Member] | Minimum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       0.00%              
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member] | Base Rate [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added       0.50%              
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES 364-Day Facility [Member]                      
Debt Instrument [Line Items]                      
Facility, maximum borrowing capacity   $ 2,000,000,000.0                  
Facility, fee rate   0.175%                  
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES 364-Day Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added   1.00%                  
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES 364-Day Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added   1.625%                  
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES 364-Day Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added   1.00%                  
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES 364-Day Facility [Member] | Percentage Above Federal Funds Effective Rate [Member] | Alternate Base Rate [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added   0.50%                  
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES 364-Day Facility [Member] | Base Rate [Member] | Minimum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added   0.00%                  
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES 364-Day Facility [Member] | Base Rate [Member] | Maximum [Member]                      
Debt Instrument [Line Items]                      
Facility, applicable margin added   0.625%                  
[1] Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2] See Note 6 and Note 15.