Condensed Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenues	$ 357,543	$ 405,232
Costs, expenses and other operating
Cost of sales (exclusive of items shown separately below)	309,906	374,999
Depreciation, depletion and amortization	25,797	31,308
Accretion on asset retirement obligations	5,437	5,006
Change in fair value of coal derivatives and coal trading activities, net	528	743
Selling, general and administrative expenses	21,480	22,745
Costs related to proposed joint venture with Peabody Energy		3,664
Asset impairment and restructuring		5,828
Gain on property insurance recovery related to Mountain Laurel longwall		(9,000)
Other operating income, net	(5,268)	(6,170)
Costs, expenses and other operating	357,880	429,123
Income (loss) from operations	(337)	(23,891)
Interest expense, net
Interest expense	(4,128)	(3,388)
Interest and investment income	328	1,259
Interest expense, net	(3,800)	(2,129)
Income (loss) before nonoperating expenses	(4,137)	(26,020)
Nonoperating (expenses) income
Non-service related pension and postretirement benefit (costs) credits	(1,527)	(1,096)
Reorganization items, net		26
Nonoperating (expenses) income	(1,527)	(1,070)
Income (loss) before income taxes	(5,664)	(27,090)
Provision for (benefit from) income taxes	378	(1,791)
Net income (loss)	$ (6,042)	$ (25,299)
Net income (loss) per common share
Basic earnings (loss) per common share (in dollars per share)	$ (0.40)	$ (1.67)
Diluted earnings (loss) per common share (in dollars per share)	$ (0.40)	$ (1.67)
Weighted average shares outstanding
Basic weighted average shares outstanding (in shares)	15,283	15,139
Diluted weighted average shares outstanding (in shares)	15,283	15,139
Dividends declared per common share (in dollars per share)		$ 0.50