Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash Flows from Operating Activities:
Net Income (Loss)	$ 30,576	$ (18,588)
Adjustments to Reconcile Net Income (Loss) to Net Cash Provided by Operating Activities:
Depreciation, Depletion and Amortization	112,096	101,098
Gain on Sale of Assets	(10,542)	(7,315)
Stock/Unit-Based Compensation	2,719	7,250
Amortization of Debt Issuance Costs	4,331	3,146
Gain on Debt Extinguishment	(789)	(16,833)
Unrealized Loss on Commodity Derivative Instruments	20,437	0
Deferred Income Taxes	(3,708)	(5,775)
Equity in Earnings of Affiliates	312	586
Changes in Operating Assets:
Accounts and Notes Receivable	45,093	42,469
Inventories	(3,099)	(6,910)
Prepaid Expenses and Other Assets	6,436	11,936
Changes in Other Assets	(345)	2,989
Changes in Operating Liabilities:
Accounts Payable	(6,995)	(37,669)
Other Operating Liabilities	2,880	(7,004)
Changes in Other Liabilities	(26,797)	(22,700)
Net Cash Provided by Operating Activities	172,605	46,680
Cash Flows from Investing Activities:
Capital Expenditures	(57,455)	(46,447)
Proceeds from Sales of Assets	11,918	689
Other Investing Activity	(182)	0
Net Cash Used in Investing Activities	(45,719)	(45,758)
Cash Flows from Financing Activities:
Proceeds from Finance Lease Obligations	0	16,293
Payments on Finance Lease Obligations	(14,625)	(11,928)
Proceeds from Long-Term Debt	75,000	0
Distributions to Noncontrolling Interest	0	(5,575)
Shares/Units Withheld for Taxes	(2,302)	(772)
Debt-Related Financing Fees	(2,368)	(9,002)
Net Cash Provided by (Used in) Financing Activities	22,467	(48,188)
Net Increase (Decrease) in Cash and Cash Equivalents and Restricted Cash	149,353	(47,266)
Cash and Cash Equivalents and Restricted Cash at Beginning of Period	50,850	80,293
Cash and Cash Equivalents and Restricted Cash at End of Period	200,203	33,027
Non-Cash Investing and Financing Activities:
Finance Lease	8,226	13,003
Other Equipment Financing	0	11,153
Term Loan A Facility [Member]
Cash Flows from Financing Activities:
Payments on Debt	(12,500)	(10,000)
Term Loan B Facility [Member]
Cash Flows from Financing Activities:
Payments on Debt	(6,223)	(1,375)
Senior Secured Second Lien Notes due 2025 [Member]
Cash Flows from Financing Activities:
Payments on Debt	(14,153)	(25,480)
Other Asset Backed Financing [Member]
Cash Flows from Financing Activities:
Payments on Debt	$ (362)	$ (349)