Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Royalties	$ 85,968	$ 72,401
Accrued Interest	41,310	26,549
Transportation Charges	17,648	15,969
Accrued Other Taxes	13,430	10,580
Deferred Revenue	10,980	10,986
Accrued Payroll & Benefits	7,070	5,009
Short-Term Incentive Compensation	5,323	20,340
Litigation Contingency	2,410	2,025
Purchased Gas Payable	428	1,528
Other	9,306	23,144
Current Portion of Long-Term Liabilities:
Asset Retirement Obligations	8,455	8,455
Salary Retirement	1,817	1,787
Total Other Accrued Liabilities	$ 204,145	$ 198,773

Accrued Transportation Charges

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Carrying value as of the balance sheet date of obligations incurred and payable for real and property taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of obligations incurred and payable for incentive compensation awarded to employees and directors or earned by them based on the terms of one or more relevant arrangements. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount of expenses incurred but not yet paid nor invoiced, and liabilities classified as other.

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Carrying value as of the balance sheet date of obligations incurred through that date and payable for royalties.

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Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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Amount of liability, recognized in statement of financial position, for defined benefit pension plan, classified as current. Excludes other postretirement benefit plan.

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Total of the carrying values as of the balance sheet date of obligations incurred through that date and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits.

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Carrying value as of the balance sheet date of obligations incurred and payable for purchases of natural gas. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying amount of reserve for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs, which is expected to be paid within one year of the date of the statement of financial position.

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