Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash Flows from Operating Activities:
Net Income	$ 655,892	$ 466,979	$ 34,110
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Depreciation, Depletion and Amortization	241,317	226,878	224,583
Stock-Based Compensation	10,046	7,890	6,632
Gain on Sale of Assets	(8,981)	(34,589)	(11,723)
Amortization of Debt Issuance Costs	5,468	8,314	8,552
Loss (Gain) on Debt Extinguishment	2,725	5,623	(657)
Deferred Income Taxes	14,121	49,387	(14,760)
Other Adjustments to Net Income	(3,418)	3,880	644
Changes in Operating Assets:
Trade and Other Receivables	36,922	(52,577)	44,707
Inventories	(21,540)	(3,020)	(6,676)
Other Current Assets	(4,673)	2,883	229
Changes in Other Assets	(11,725)	(26,063)	(13,797)
Changes in Operating Liabilities:
Accounts Payable	11,449	39,235	11,473
Commodity Derivatives, net Liability	(15,142)	(37,062)	52,204
Other Operating Liabilities	3,063	14,453	27,461
Changes in Other Liabilities	(57,575)	(21,221)	(57,413)
Net Cash Provided by Operating Activities	857,949	650,990	305,569
Cash Flows from Investing Activities:
Capital Expenditures	(167,791)	(171,506)	(132,752)
Proceeds from Sales of Assets	4,255	21,538	13,572
Investments in Mining-Related Activities	(7,481)	0	0
Proceeds from Sales of Short-Term Investments	122,658	0	0
Purchases of Short-Term Investments	(200,870)	0	0
Other Investing Activity	(10,203)	7,790	(8,181)
Net Cash Used in Investing Activities	(259,432)	(142,178)	(127,361)
Cash Flows from Financing Activities:
Payments on Finance Lease Obligations	(25,335)	(24,511)	(27,447)
Proceeds from Long-Term Debt	0	0	75,000
Payments on Other Debt	(981)	(840)	(731)
Shares Withheld for Taxes	(12,831)	(6,261)	(2,303)
Repurchases of Common Stock	(399,379)	0	0
Debt Issuance and Financing Fees	(2,779)	(7,957)	(2,368)
Dividends	(75,474)	(71,486)	0
Net Cash Used in Financing Activities	(682,201)	(380,066)	(30,852)
Net (Decrease) Increase in Cash and Cash Equivalents and Restricted Cash	(83,684)	128,746	147,356
Cash and Cash Equivalents and Restricted Cash at Beginning of Period	326,952	198,206	50,850
Cash and Cash Equivalents and Restricted Cash at End of Period	243,268	326,952	198,206
Term Loan A Facility
Cash Flows from Financing Activities:
Payments on Debt	0	(41,250)	(25,000)
Term Loan B Facility
Cash Flows from Financing Activities:
Payments on Debt	(63,590)	(175,687)	(30,911)
Senior Secured Second Lien Notes due 2025
Cash Flows from Financing Activities:
Payments on Debt	$ (101,832)	$ (52,074)	$ (17,092)