Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Royalties	$ 70,803	$ 74,061
Accrued Interest	25,800	30,862
Transportation Charges	22,355	16,533
Deferred Revenue	12,123	13,964
Short-Term Incentive Compensation	2,626	21,030
Accrued Other Taxes	9,385	9,115
Accrued Payroll & Benefits	6,209	6,248
Other	41,145	37,610
Current Portion of Long-Term Liabilities:
Asset Retirement Obligations	5,076	5,076
Salary Retirement	1,608	1,587
Total Other Accrued Liabilities	$ 197,130	$ 216,086