Quarterly report pursuant to Section 13 or 15(d)

Borrowings (Schedule of Borrowings) (Details)

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Borrowings (Schedule of Borrowings) (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
May 19, 2017
Principal components:      
Total principal outstanding $ 1,065,000 $ 625,000  
Premium on senior unsecured notes, net of accumulated amortization 6,750 7,594  
Unamortized deferred financing costs (18,222) (12,398)  
Total carrying value of borrowings 1,053,528 620,196  
Senior secured revolving credit facility      
Principal components:      
Total principal outstanding 65,000 25,000  
6.125% senior unsecured notes due 2024      
Principal components:      
Total principal outstanding $ 600,000 600,000  
Debt instrument, interest rate, stated (as a percent) 6.125%   6.125%
6.375% senior unsecured notes due 2026      
Principal components:      
Total principal outstanding $ 400,000 $ 0  
Debt instrument, interest rate, stated (as a percent) 6.375%