Annual report pursuant to Section 13 and 15(d)

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

v3.20.4
Fair Value Measurements (Summary of Financial Instruments at Carrying and Fair Value) (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Sep. 30, 2020
Dec. 31, 2019
Dec. 20, 2019
Aug. 31, 2018
Jun. 07, 2018
Oct. 03, 2016
9.00% Second Lien Notes              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Debt instrument, interest rate, stated (as a percent) 9.00% 9.00%          
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%
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%            
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 $ 2,027,641   $ 1,900,000        
Principal Amount | Unsecured debt | 9.00% Second Lien Notes              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 516,659   0        
Principal Amount | Unsecured debt | 6.25% Senior Notes due 2023              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 542,720   650,000        
Principal Amount | Unsecured debt | 6.125% Senior Notes due 2024              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 460,241   600,000        
Principal Amount | Unsecured debt | 8.25% Senior Notes due 2025              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 187,238   250,000        
Principal Amount | Unsecured debt | 6.375% Senior Notes due 2026              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 320,783   400,000        
Fair Value              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Total 1,336,990   1,930,929        
Fair Value | Unsecured debt | 9.00% Second Lien Notes              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 470,160   0        
Fair Value | Unsecured debt | 6.25% Senior Notes due 2023              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 344,627   658,125        
Fair Value | Unsecured debt | 6.125% Senior Notes due 2024              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 260,036   611,130        
Fair Value | Unsecured debt | 8.25% Senior Notes due 2025              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes 100,172   256,250        
Fair Value | Unsecured debt | 6.375% Senior Notes due 2026              
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]              
Senior Notes $ 161,995   $ 405,424