Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Summary of Financial Instruments at Carrying and Fair Value) (Details)

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Fair Value Measurements (Summary of Financial Instruments at Carrying and Fair Value) (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Jun. 07, 2018
May 19, 2017
Oct. 03, 2016
6.125% senior unsecured notes due 2024          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Debt instrument, interest rate, stated (as a percent) 6.125%        
6.125% senior unsecured notes due 2024 | Unsecured debt          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Debt instrument, interest rate, stated (as a percent) 6.125%     6.125% 6.125%
6.375% senior unsecured notes due 2026          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Debt instrument, interest rate, stated (as a percent) 6.375%        
6.375% senior unsecured notes due 2026 | Unsecured debt          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Debt instrument, interest rate, stated (as a percent) 6.375%   6.375%    
Carrying Value          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Credit Facility $ 330,000 $ 200,000      
Total 1,319,867 1,189,473      
Carrying Value | 6.125% senior unsecured notes due 2024 | Unsecured debt          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Senior Notes 595,971 595,788      
Carrying Value | 6.375% senior unsecured notes due 2026 | Unsecured debt          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Senior Notes 393,896 393,685      
Fair Value          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Credit Facility 330,000 200,000      
Total 1,336,272 1,130,000      
Fair Value | 6.125% senior unsecured notes due 2024 | Unsecured debt          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Senior Notes 604,008 558,000      
Fair Value | 6.375% senior unsecured notes due 2026 | Unsecured debt          
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]          
Senior Notes $ 402,264 $ 372,000