CONDENSED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Total revenues	$ 180,064	$ 287,506	$ 570,484	$ 1,063,408
Costs and expenses:
Cost of sales (exclusive of items shown separately below)	151,370	190,221	433,661	578,038
Cost of other revenues (exclusive of items shown separately below)	7,064	7,583	22,267	23,346
Depreciation and depletion	27,965	25,741	78,813	73,652
Selling, general and administrative	8,192	9,362	25,105	29,050
Total costs and expenses	194,591	232,907	559,846	704,086
Operating income (loss)	(14,527)	54,599	10,639	359,322
Interest expense, net	(8,059)	(7,250)	(23,847)	(22,793)
Loss on early extinguishment of debt	0	0	0	(9,756)
Other income	0	5,272	1,822	22,815
Income (loss) before income tax expense (benefit)	(22,586)	52,621	(11,386)	349,588
Income tax expense (benefit)	(8,152)	7,599	(9,336)	68,639
Net income (loss)	$ (14,434)	$ 45,022	$ (2,050)	$ 280,949
Basic and diluted net income (loss) per share:
Net income (loss) per share-basic (in dollars per share)	$ (0.28)	$ 0.88	$ (0.04)	$ 5.46
Net income (loss) per share-diluted (in dollars per share)	$ (0.28)	$ 0.87	$ (0.04)	$ 5.44
Weighted average number of shares outstanding-basic (in shares)	51,190	51,348	51,161	51,469
Weighted average number of shares outstanding-diluted (in shares)	51,356	51,482	51,275	51,599
Dividends per share (in dollars per share)	$ 0.05	$ 0.05	$ 0.15	$ 4.56
Sales
Revenues:
Total revenues	$ 175,229	$ 280,841	$ 555,610	$ 1,037,950
Other revenues
Revenues:
Total revenues	$ 4,835	$ 6,665	$ 14,875	$ 25,458