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, 2019
Dec. 20, 2019
Dec. 31, 2018
Jun. 07, 2018
Dec. 31, 2017
May 19, 2017
Oct. 03, 2016
6.25% Senior Notes due 2023              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Debt instrument, interest rate, stated (as a percent) 6.25% 6.25%         6.25%
6.125% Senior 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% 6.125%
8.25% Senior Notes due 2025              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Debt instrument, interest rate, stated (as a percent) 8.25% 8.25%          
6.375% Senior 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%        
Unsecured debt | 6.375% Senior 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%      
Principal Amount              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Total $ 1,900,000   $ 1,000,000        
Principal Amount | Unsecured debt | 6.25% Senior Notes due 2023              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 650,000   0        
Principal Amount | Unsecured debt | 6.125% Senior Notes due 2024              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 600,000   600,000        
Principal Amount | Unsecured debt | 8.25% Senior Notes due 2025              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 250,000   0        
Principal Amount | Unsecured debt | 6.375% Senior Notes due 2026              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 400,000   400,000        
Fair Value              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Total 1,930,929   930,000        
Fair Value | Unsecured debt | 6.25% Senior Notes due 2023              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 658,125   0        
Fair Value | Unsecured debt | 6.125% Senior Notes due 2024              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 611,130   558,000        
Fair Value | Unsecured debt | 8.25% Senior Notes due 2025              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 256,250   0        
Fair Value | Unsecured debt | 6.375% Senior Notes due 2026              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes $ 405,424   $ 372,000