Annual report pursuant to Section 13 and 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
Dec. 31, 2018
Dec. 31, 2017
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% 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%      
Unsecured debt | 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%      
Carrying Value        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Credit facility $ 200,000 $ 25,000    
Total 1,189,473 620,196    
Carrying Value | Unsecured debt | 6.125% senior unsecured notes due 2024        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Senior Notes 595,788 595,196    
Carrying Value | Unsecured debt | 6.375% senior unsecured notes due 2026        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Senior Notes $ 393,685 0    
Debt instrument, interest rate, stated (as a percent) 6.375%      
Fair Value        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Credit facility $ 200,000 25,000    
Total 1,130,000 643,000    
Fair Value | Unsecured debt | 6.125% senior unsecured notes due 2024        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Senior Notes 558,000 618,000    
Fair Value | Unsecured debt | 6.375% senior unsecured notes due 2026        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Senior Notes $ 372,000 $ 0