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Long-Term Debt - By Issue (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2017
Long Term Debt
Total debt	$ 2,764,472	$ 2,401,393
Less debt issuance costs	30,128	24,670
Long-term Debt, Total	2,734,344	2,376,723
Less current maturities	89,356	24,234
Long-term debt	2,644,988	2,352,489
5 1/4% Senior Notes due 2023
Long Term Debt
Total debt	$ 400,000	400,000
Stated interest rate	5.25%
2.800% senior notes due 2024
Long Term Debt
Total debt	$ 400,000
Stated interest rate	2.80%
5.500% senior notes due 2024
Long Term Debt
Total debt	$ 500,000	500,000
Stated interest rate	5.50%
4.125% senior notes due 2025
Long Term Debt
Total debt	$ 350,000	350,000
Stated interest rate	4.125%		4.125%
5.000% senior notes due 2026
Long Term Debt
Total debt	$ 400,000	400,000
Stated interest rate	5.00%
3.450% senior notes due 2030
Long Term Debt
Total debt	$ 600,000
Stated interest rate	3.45%
5.125% senior notes due 2021
Long Term Debt
Total debt		700,000
Stated interest rate	5.125%
Other obligations
Long Term Debt
Total debt	$ 114,472	$ 51,393
6.375% senior notes due 2022
Long Term Debt
Stated interest rate	6.375%