Business Segments (Tables)

6 Months Ended

Jun. 30, 2019

Segment Reporting [Abstract]

Segment Reporting Information

	THREE MONTHS ENDED						SIX MONTHS ENDED
	JUNE 30						JUNE 30
	2019			2018			2019			2018
Revenues
Coal Mining	$	22,570		$	20,860		$	39,320		$	38,457
NAMining	10,728			9,067			21,503			19,280
Minerals Management	8,242			3,866			20,928			7,342
Unallocated Items	131			—			674			—
Eliminations	(319		)	(112		)	(976		)	(198		)
Total	$	41,352		$	33,681		$	81,449		$	64,881
Operating profit (loss)
Coal Mining	$	4,693		$	7,898		$	12,298		$	16,595
NAMining	(483		)	157			(451		)	791
Minerals Management	6,789			3,212			18,458			6,156
Unallocated Items	(2,130		)	(3,465		)	(4,829		)	(6,019		)
Eliminations	292			—			58			—
Total	$	9,161		$	7,802		$	25,534		$	17,523

Expenditures for property, plant and equipment
Coal Mining	$	1,623	$	3,850	$	5,493	$	4,426
NAMining	—		2,557		—		3,231
Minerals Management	50		150		291		1,182
Unallocated Items	42		173		183		343
Total	$	1,715	$	6,730	$	5,967	$	9,182
Depreciation, depletion and amortization
Coal Mining	$	3,276	$	3,092	$	6,150	$	5,933
NAMining	566		427		1,111		822
Minerals Management	367		178		733		312
Unallocated Items	29		27		57		53
Total	$	4,238	$	3,724	$	8,051	$	7,120