Quarterly report pursuant to Section 13 or 15(d)

Borrowings (Credit Facility) (Narrative) (Details)

v3.10.0.1
Borrowings (Credit Facility) (Narrative) (Details)
9 Months Ended
Apr. 05, 2018
USD ($)
May 25, 2017
USD ($)
lender
Sep. 30, 2018
USD ($)
Sep. 27, 2018
USD ($)
Dec. 31, 2017
USD ($)
Line of Credit Facility [Line Items]          
Balance outstanding on credit facility     $ 65,000,000   $ 25,000,000
Senior secured revolving credit facility | Secured debt          
Line of Credit Facility [Line Items]          
Debt instrument maturity date May 25, 2023 May 25, 2022      
Institutional lenders | lender   17      
Maximum borrowing capacity   $ 2,000,000,000      
Credit facility borrowing base $ 825,000,000   1,100,000,000 $ 1,100,000,000  
Increase limit $ 650,000,000   850,000,000 $ 850,000,000  
Balance outstanding on credit facility     65,000,000    
Letters of credit outstanding     $ 17,675,000    
Interest rate at period end (as a percent)     3.29%    
Unused capacity, commitment fee (as a percent)     0.375%    
Senior secured revolving credit facility | Secured debt | Minimum          
Line of Credit Facility [Line Items]          
Debt instrument interest rate (as a percent) 1.25%   1.25%    
Senior secured revolving credit facility | Secured debt | Maximum          
Line of Credit Facility [Line Items]          
Debt instrument interest rate (as a percent) 2.25%   2.25%