Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 287,807	$ 236,059
Short-term investments	32,724	36,993
Restricted cash	1,100	1,100
Trade accounts receivable (net of $0 allowance at December 31, 2023 and December 31, 2022)	273,522	236,999
Other receivables	13,700	18,301
Inventories	244,261	223,015
Other current assets	64,653	71,384
Total current assets	917,767	823,851
Property, plant and equipment, net
Coal lands and mineral rights	402,387	406,085
Plant and equipment	1,099,511	968,420
Deferred mine development	509,637	475,037
Property, plant and equipment, gross	2,011,535	1,849,542
Less accumulated depreciation, depletion and amortization	(782,644)	(662,514)
Property, plant and equipment, net	1,228,891	1,187,028
Other assets
Deferred income taxes	124,024	209,470
Equity investments	22,815	17,267
Fund for asset retirement obligations	142,266	135,993
Other noncurrent assets	48,410	59,499
Total other assets	337,515	422,229
Total assets	2,484,173	2,433,108
Current Liabilities
Accounts payable	205,001	211,848
Accrued expenses and other current liabilities	127,617	157,043
Current maturities of debt	35,343	57,988
Total current liabilities	367,961	426,879
Long-term debt	105,252	116,288
Asset retirement obligations	255,740	235,736
Accrued pension benefits	878	1,101
Accrued postretirement benefits other than pension	47,494	49,674
Accrued workers' compensation	154,650	155,756
Other noncurrent liabilities	72,742	82,094
Total liabilities	1,004,717	1,067,528
Stockholders' equity
Common stock, $0.01 par value, authorized 300,000 shares, issued 30,557 and 28,761 shares at December 31, 2023 and December 31, 2022, respectively	306	288
Paid-in capital	720,029	724,660
Retained earnings	1,830,018	1,565,374
Treasury stock, 12,197 and 11,207 shares at December 31, 2023 and December 31, 2022, respectively, at cost	(1,109,679)	(986,171)
Accumulated other comprehensive income	38,782	61,429
Total stockholders' equity	1,479,456	1,365,580
Total liabilities and stockholders' equity	$ 2,484,173	$ 2,433,108