Quarterly report pursuant to Section 13 or 15(d)

Borrowings (Credit Facility) (Narrative) (Details)

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Borrowings (Credit Facility) (Narrative) (Details)
3 Months Ended
Apr. 05, 2018
USD ($)
May 25, 2017
USD ($)
lender
Mar. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Line of Credit Facility [Line Items]        
Balance outstanding on credit facility     $ 75,000,000 $ 25,000,000
Senior secured revolving credit facility        
Line of Credit Facility [Line Items]        
Debt instrument maturity date   May 25, 2022    
Institutional lenders | lender   17    
Maximum borrowing capacity   $ 2,000,000,000    
Increase limit     700,000,000  
Credit facility borrowing base     500,000,000  
Balance outstanding on credit facility     75,000,000  
Letters of credit outstanding     $ 1,250,000  
Interest rate at period end (as a percent)     3.75%  
Unused capacity, commitment fee (as a percent)     0.375%  
Senior secured revolving credit facility | Subsequent Event        
Line of Credit Facility [Line Items]        
Debt instrument maturity date May 25, 2023      
Increase limit $ 825,000,000      
Credit facility borrowing base $ 650,000,000      
Senior secured revolving credit facility | Minimum        
Line of Credit Facility [Line Items]        
Debt instrument interest rate (as a percent)     2.00%  
Senior secured revolving credit facility | Minimum | Subsequent Event        
Line of Credit Facility [Line Items]        
Debt instrument interest rate (as a percent) 1.25%      
Senior secured revolving credit facility | Maximum        
Line of Credit Facility [Line Items]        
Debt instrument interest rate (as a percent)     3.00%  
Senior secured revolving credit facility | Maximum | Subsequent Event        
Line of Credit Facility [Line Items]        
Debt instrument interest rate (as a percent) 2.25%