Long-term debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total principal long-term debt	$ 3,483,000	$ 3,582,000
Debt issuance costs	(34,399)	(36,595)
Unamortized premiums and discounts, net	7,377	7,815
Total long-term debt	3,455,978	3,553,220
Borrowings under revolving credit agreement expiring August 2024
Debt Instrument [Line Items]
Total principal long-term debt	$ 256,000	$ 355,000
Unsecured notes bearing fixed rate interest at 5.500% due September 2024 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate (as a percent)	0.055%	0.055%
Total principal long-term debt	$ 137,000	$ 137,000
Unsecured notes bearing fixed rate interest at 4.750% due March 2026 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate (as a percent)	0.0475%	0.0475%
Total principal long-term debt	$ 550,000	$ 550,000
Unsecured notes bearing fixed rate interest at 7.75% due June 2027 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate (as a percent)	0.0775%	0.0775%
Total principal long-term debt	$ 200,000	$ 200,000
Unsecured notes bearing fixed rate interest at 7.25% due September 2027 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate (as a percent)	0.0725%	0.0725%
Total principal long-term debt	$ 240,000	$ 240,000
Unsecured notes bearing fixed rate interest at 4.625% due March 2028 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate (as a percent)	0.04625%	0.04625%
Total principal long-term debt	$ 1,000,000	$ 1,000,000
Unsecured notes bearing fixed rate interest at 5.00% due September 2029 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate (as a percent)	0.05%	0.05%
Total principal long-term debt	$ 1,100,000	$ 1,100,000