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Long-Term Debt - By Issue (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Long Term Debt
Total debt	$ 2,401,393	$ 2,408,852
Less debt issuance costs	24,670	26,912
Total amounts outstanding	2,376,723	2,381,940
Less current maturities	24,234	28,795
Long-term debt	2,352,489	2,353,145
5.125% senior notes due 2021
Long Term Debt
Total debt	700,000	700,000
Total amounts outstanding	$ 700,000
Stated interest rate	5.125%
5 1/4% Senior Notes due 2023
Long Term Debt
Total debt	$ 400,000	400,000
Total amounts outstanding	$ 400,000
Stated interest rate	5.25%
5.500% senior notes due 2024
Long Term Debt
Total debt	$ 500,000	500,000
Total amounts outstanding	$ 500,000
Stated interest rate	5.50%
4.125% Senior Note due 2025 [Member]
Long Term Debt
Total debt	$ 350,000	350,000
Total amounts outstanding	$ 350,000
Stated interest rate	4.125%		4.125%
Senior Notes 5.000 Percent Due 2026 [Member]
Long Term Debt
Total debt	$ 400,000	400,000
Total amounts outstanding	$ 400,000
Stated interest rate	5.00%
6 3/8% Senior Notes, due 2022
Long Term Debt
Stated interest rate	6.375%
6 1/8% senior notes, due 2019
Long Term Debt
Stated interest rate	6.125%
Other obligations
Long Term Debt
Total debt	$ 51,393	58,852
Parent Company [Member]
Long Term Debt
Less current maturities	793	731
Long-term debt	2,327,798	2,326,466
Guarantors
Long Term Debt
Less current maturities	1,355
Long-term debt	381
Combined Non-Guarantors
Long Term Debt
Less current maturities	51,079	56,454
Long-term debt	$ 166,226	$ 169,799