Revenue Recognition (Tables)

6 Months Ended

Jun. 30, 2020

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The following table disaggregates revenue by major sources:

	THREE MONTHS ENDED						SIX MONTHS ENDED
	JUNE 30						JUNE 30
Major Goods/Service Lines	2020			2019			2020			2019
Coal Mining	$	21,573		$	22,570		$	42,501		$	39,320
NAMining	12,048			10,728			23,672			21,503
Minerals Management	1,987			8,242			7,228			20,928
Unallocated Items	327			131			353			674
Eliminations	(580		)	(319		)	(755		)	(976		)
Total revenues	$	35,355		$	41,352		$	72,999		$	81,449
Timing of Revenue Recognition
Goods transferred at a point in time	$	20,976		$	21,879		$	41,260		$	37,964
Services transferred over time	14,379			19,473			31,739			43,485
Total revenues	$	35,355		$	41,352		$	72,999		$	81,449

Contract Balances

The opening and closing balances of the Company’s current and long-term contract liabilities and receivables are as follows:

	Contract balances
	Trade accounts receivable, net		Contract liability (current)			Contract liability (long-term)
Balance, January 1, 2020	$	15,444	$	944		$	2,153
Balance, June 30, 2020	20,335		941			1,683
Increase (decrease)	$	4,891	$	(3	)	$	(470	)