Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 325,194	$ 187,492
Short-term investments	14,463	96,765
Restricted cash	1,101	5,953
Trade accounts receivable (net of $0 allowance at December 31, 2021 and December 31, 2020)	324,304	110,869
Other receivables	8,271	3,053
Inventories	156,734	126,008
Other current assets	52,804	58,000
Total current assets	882,871	588,140
Property, plant and equipment
Coal lands and mineral rights	406,822	406,095
Plant and equipment	844,107	734,194
Deferred mine development	402,470	288,693
Property, plant and equipment, gross	1,653,399	1,428,982
Less accumulated depreciation, depletion and amortization	(533,356)	(421,679)
Property, plant and equipment, net	1,120,043	1,007,303
Other assets
Equity investments	15,403	71,783
Fund for asset retirement obligations	20,000
Other noncurrent assets	78,843	55,246
Total other assets	114,246	127,029
Total assets	2,117,160	1,722,472
Current Liabilities
Accounts payable	131,986	103,743
Accrued expenses and other current liabilities	167,304	155,256
Current maturities of debt	223,050	31,097
Total current liabilities	522,340	290,096
Long-term debt	337,623	477,215
Asset retirement obligations	192,672	230,732
Accrued pension benefits	1,300	2,879
Accrued postretirement benefits other than pension	73,565	94,388
Accrued workers' compensation	224,105	244,695
Other noncurrent liabilities	81,689	98,906
Total liabilities	1,433,294	1,438,911
Stockholders' equity
Common stock, $0.01 par value, authorized 300,000 shares, issued 25,481 and 25,323 shares at December 31, 2021 and December 31, 2020, respectively	255	253
Paid-in capital	784,356	767,484
Retained earnings	712,478	378,906
Treasury stock, 10,088 shares at December 31, 2021 and December 31, 2020, respectively, at cost	(827,381)	(827,381)
Accumulated other comprehensive income (loss)	14,158	(35,701)
Total stockholders' equity	683,866	283,561
Total liabilities and stockholders' equity	$ 2,117,160	$ 1,722,472