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Debt and Interest Expense - Additional Information (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Mar. 31, 2019
Jun. 30, 2019
Jun. 30, 2018
Jul. 01, 2019
Feb. 28, 2019
Dec. 31, 2018
Dec. 19, 2018
Feb. 16, 2018
Jun. 30, 2017
Debt Instrument [Line Items]                    
APCWH Note Payable, maximum borrowing [1] $ 0   $ 0       $ 427,493,000 [2]      
Gain (loss) on interest-rate swaps     (94,585,000) $ 0 [2]            
WES [Member] | Revolving Credit Facility [Member] | WGP RCF [Member]                    
Debt Instrument [Line Items]                    
Facility, maximum borrowing capacity                 $ 35,000,000.0  
Facility, Repayment of borrowings   $ 28,000,000.0 28,000,000              
WES Operating [Member]                    
Debt Instrument [Line Items]                    
APCWH Note Payable, maximum borrowing [3] 0   0       427,493,000 [2]      
Gain (loss) on interest-rate swaps     (94,585,000) $ 0 [2]            
WES Operating [Member] | Interest-Rate Swap [Member]                    
Debt Instrument [Line Items]                    
Gain (loss) on interest-rate swaps 59,000,000.0   94,600,000              
WES Operating [Member] | Not Designated as Hedging Instrument [Member]                    
Debt Instrument [Line Items]                    
Interest-rate swap, notional amount   $ 375,000,000.0         750,000,000.0      
WES Operating [Member] | Not Designated as Hedging Instrument [Member] | Interest-Rate Swap [Member]                    
Debt Instrument [Line Items]                    
Interest-rate swap, collateral posted if credit risk related provision triggered 44,000,000.0   44,000,000.0              
Interest-rate swap, aggregate fair value of swaps with credit risk related features for which a net liability position existed 82,300,000   82,300,000       5,700,000      
WES Operating [Member] | Not Designated as Hedging Instrument [Member] | Interest-Rate Swap [Member] | Accrued Liabilities [Member]                    
Debt Instrument [Line Items]                    
Interest-rate swap, liability fair value 102,600,000   $ 102,600,000       $ 8,000,000.0      
WES Operating [Member] | APCWH Note Payable [Member]                    
Debt Instrument [Line Items]                    
APCWH Note Payable, interest rate       2.83%            
WES Operating [Member] | APCWH Note Payable [Member] | Maximum [Member]                    
Debt Instrument [Line Items]                    
APCWH Note Payable, maximum borrowing                   $ 500,000,000.0
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member]                    
Debt Instrument [Line Items]                    
Facility, maximum borrowing capacity           $ 2,000,000,000.0     $ 1,500,000,000  
Facility, accordion feature amount           500,000,000        
Facility, expandable maximum borrowing capacity           $ 2,500,000,000        
Facility, fee rate     0.20% 0.20%            
Facility, outstanding borrowings 920,000,000.0   $ 920,000,000.0              
Facility, available borrowing capacity $ 1,100,000,000   $ 1,100,000,000              
Facility, interest rate at period end 3.71%   3.71% 3.39%            
Facility, outstanding letters of credit $ 4,600,000   $ 4,600,000              
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member] | Minimum [Member]                    
Debt Instrument [Line Items]                    
Facility, fee rate     0.125%              
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member] | Maximum [Member]                    
Debt Instrument [Line Items]                    
Facility, fee rate     0.25%              
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     1.00%              
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     1.50%              
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member] | London Interbank Offered Rate (LIBOR) [Member] | Alternate Base Rate [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     1.00%              
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member] | Percentage Above Federal Funds Effective Rate [Member] | Alternate Base Rate [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     0.50%              
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member] | Base Rate [Member] | Minimum [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     0.00%              
WES Operating [Member] | Revolving Credit Facility [Member] | RCF [Member] | Base Rate [Member] | Maximum [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     0.50%              
WES Operating [Member] | Revolving Credit Facility [Member] | Term Loan Facility [Member]                    
Debt Instrument [Line Items]                    
Facility, maximum borrowing capacity               $ 2,000,000,000.0    
Facility, outstanding borrowings $ 2,000,000,000.0   $ 2,000,000,000.0              
Facility, interest rate at period end 3.78%   3.78%              
WES Operating [Member] | Revolving Credit Facility [Member] | Term Loan Facility [Member] | Subsequent Event [Member]                    
Debt Instrument [Line Items]                    
Facility, maximum borrowing capacity         $ 3,000,000,000.0          
Facility, incremental capacity with provision carve out         $ 1,000,000,000.0          
WES Operating [Member] | Revolving Credit Facility [Member] | Term Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     1.00%              
WES Operating [Member] | Revolving Credit Facility [Member] | Term Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     1.625%              
WES Operating [Member] | Revolving Credit Facility [Member] | Term Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Alternate Base Rate [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     1.00%              
WES Operating [Member] | Revolving Credit Facility [Member] | Term Loan Facility [Member] | Percentage Above Federal Funds Effective Rate [Member] | Alternate Base Rate [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     0.50%              
WES Operating [Member] | Revolving Credit Facility [Member] | Term Loan Facility [Member] | Base Rate [Member] | Minimum [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     0.00%              
WES Operating [Member] | Revolving Credit Facility [Member] | Term Loan Facility [Member] | Base Rate [Member] | Maximum [Member]                    
Debt Instrument [Line Items]                    
Facility, applicable margin added     0.625%              
[1]
See Note 1 and Note 6.
[2]
Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[3]
See Note 1 and Note 6.