Supplemental Disclosures to the Financial Statements - Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accounts payable-trade	$ 8,086	$ 13,986
Accrued expenses	40,211	57,078
Royalties payable	10,647	25,385
Taxes other than income tax liability	9,586	9,150
Accrued interest	10,500	10,500
Dividends payable	32	9,888
Asset retirement obligation - current portion	13,700	25,208
Other	1,925	616
Total accounts payable and accrued expenses	$ 94,687	$ 151,811