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Long-term debt - Narrative (Detail)
12 Months Ended
Oct. 13, 2020
USD ($)
Jun. 11, 2020
Jun. 10, 2020
Feb. 11, 2020
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Sep. 10, 2020
USD ($)
Jan. 09, 2020
USD ($)
Debt Instrument [Line Items]                  
Repayments of debt         $ 1,623,000,000 $ 710,000,000 $ 121,146,000    
Borrowings under revolving credit facility expiring August 2024                  
Debt Instrument [Line Items]                  
Covenant requirement, maximum total leverage ratio   5.25 5.50            
Senior Notes                  
Debt Instrument [Line Items]                  
Early redemption fee       $ 13,800,000          
Write off of unamortized financing fees and discounts       7,900,000          
Senior Notes | Senior Notes Bearing Interest at 4.625 Percent Due March 2028                  
Debt Instrument [Line Items]                  
Debt instrument, face amount       $ 1,000,000,000.0         $ 1,000,000,000.0
Interest rate stated percentage                 4.625%
Senior Notes | Unsecured notes bearing fixed rate interest at 5.125% due July 2020                  
Debt Instrument [Line Items]                  
Interest rate stated percentage       5.125% 5.125%        
Repayments of unsecured debt       $ 310,000,000.0          
Senior Notes | Unsecured notes bearing fixed rate interest at 6.375% due October 2023                  
Debt Instrument [Line Items]                  
Interest rate stated percentage       6.375% 6.375%        
Repayments of unsecured debt       $ 650,000,000.0          
Senior Notes | Unsecured notes bearing fixed rate interest at 4.75% due March 2026                  
Debt Instrument [Line Items]                  
Debt instrument, face amount               $ 550,000,000  
Interest rate stated percentage         4.75%     4.75%  
Senior Notes | Unsecured notes bearing fixed rate interest at 4.875% due September 2021                  
Debt Instrument [Line Items]                  
Interest rate stated percentage 4.875%       4.875%        
Repayments of debt $ 350,000,000                
Senior Notes | Unsecured notes bearing fixed rate interest at 5.50% due September 2024                  
Debt Instrument [Line Items]                  
Interest rate stated percentage 5.50%       5.50%        
Repayments of debt $ 188,000,000                
Redemption premium $ 3,400,000                
Revolving Credit Facility | Line of Credit                  
Debt Instrument [Line Items]                  
Unused borrowing capacity         $ 1,130,000,000