CONDENSED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Total revenues	$ 202,467	$ 180,064	$ 643,671	$ 570,485
Costs and expenses:
Cost of sales (exclusive of items shown separately below)	91,973	151,370	399,088	433,661
Cost of other revenues (exclusive of items shown separately below)	6,654	7,064	22,792	22,267
Depreciation and depletion	28,967	27,965	102,021	78,813
Selling, general and administrative	7,430	8,192	26,182	25,105
Business interruption	6,872	0	13,892	0
Idle mine	9,327	0	20,203	0
Total costs and expenses	151,223	194,591	584,178	559,846
Operating income (loss)	51,244	(14,527)	59,493	10,639
Interest expense, net	(8,784)	(8,059)	(25,954)	(23,847)
Other income	1,400	0	1,291	1,822
Income (loss) before income tax expense (benefit)	43,860	(22,586)	34,830	(11,386)
Income tax expense (benefit)	5,433	(8,152)	22,439	(9,336)
Net income (loss)	$ 38,427	$ (14,434)	$ 12,391	$ (2,050)
Basic and diluted net income (loss) per share:
Net income (loss) per share-basic (in dollars per share)	$ 0.75	$ (0.28)	$ 0.24	$ (0.04)
Net income (loss) per share-diluted (in dollars per share)	$ 0.74	$ (0.28)	$ 0.24	$ (0.04)
Weighted average number of shares outstanding-basic (in shares)	51,416	51,190	51,315	51,161
Weighted average number of shares outstanding-diluted (in shares)	51,585	51,190	51,424	51,161
Dividends per share (in dollars per share)	$ 0.05	$ 0.05	$ 0.15	$ 0.15
Sales
Revenues:
Total revenues	$ 199,745	$ 175,229	$ 631,493	$ 555,610
Other revenues
Revenues:
Total revenues	$ 2,722	$ 4,835	$ 12,178	$ 14,875