Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash Flows from Operating Activities:
Net Income	$ 26,404	$ 2,475
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Depreciation, Depletion and Amortization	59,897	54,943
(Gain) Loss on Sale of Assets	(8,202)	14
Stock/Unit-Based Compensation	1,509	5,014
Amortization of Debt Issuance Costs	2,140	1,444
Gain on Debt Extinguishment	(683)	(16,833)
Deferred Income Taxes	5,185	1,908
Equity in Earnings of Affiliates	206	315
Changes in Operating Assets:
Accounts and Notes Receivable	(5,764)	23,064
Inventories	475	(4,507)
Prepaid Expenses and Other Assets	1,620	4,845
Changes in Other Assets	(1,459)	191
Changes in Operating Liabilities:
Accounts Payable	(73)	(15,726)
Other Operating Liabilities	9,242	3,899
Changes in Other Liabilities	(12,501)	(9,646)
Net Cash Provided by Operating Activities	77,996	51,400
Cash Flows from Investing Activities:
Capital Expenditures	(13,800)	(27,178)
Proceeds from Sales of Assets	8,488	0
Other Investing Activity	(182)	0
Net Cash Used in Investing Activities	(5,494)	(27,178)
Cash Flows from Financing Activities:
Proceeds from Finance Lease Obligations	0	16,293
Payments on Finance Lease Obligations	(8,498)	(4,899)
Distributions to Noncontrolling Interest	0	(5,575)
Shares/Units Withheld for Taxes	(2,072)	(772)
Debt-Related Financing Fees	0	(643)
Net Cash Used in Financing Activities	(31,875)	(25,688)
Net Increase (Decrease) in Cash and Cash Equivalents and Restricted Cash	40,627	(1,466)
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	91,477	78,827
Non-Cash Investing and Financing Activities:
Finance Lease	8,226	7,023
Other Equipment Financing	0	9,129
Term Loan A Facility [Member]
Cash Flows from Financing Activities:
Payments on Debt	(6,250)	(3,750)
Term Loan B Facility [Member]
Cash Flows from Financing Activities:
Payments on Debt	(5,536)	(688)
Senior Secured Second Lien Notes due 2025 [Member]
Cash Flows from Financing Activities:
Payments on Debt	(9,338)	(25,480)
Other Asset Backed Financing [Member]
Cash Flows from Financing Activities:
Payments on Debt	$ (181)	$ (174)