Revenue Recognition (Tables)

9 Months Ended

Sep. 30, 2019

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The following table disaggregates revenue by major sources:

	THREE MONTHS ENDED						NINE MONTHS ENDED
	SEPTEMBER 30						SEPTEMBER 30
Major Goods/Service Lines	2019			2018			2019			2018
Coal Mining	$	18,799		$	18,583		$	58,119		$	57,040
NAMining	8,993			9,092			30,496			28,372
Minerals Management	5,022			3,902			25,950			11,244
Unallocated Items	52			—			726			—
Eliminations	(263		)	(137		)	(1,239		)	(335		)
Total revenues	$	32,603		$	31,440		$	114,052		$	96,321
Timing of Revenue Recognition
Goods transferred at a point in time	$	18,049		$	17,975		$	56,012		$	55,170
Services transferred over time	14,554			13,465			58,040			41,151
Total revenues	$	32,603		$	31,440		$	114,052		$	96,321

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, 2019	$	20,817		$	754		$	2,008
Balance, September 30, 2019	13,540			726			1,543
Increase (decrease)	$	(7,277	)	$	(28	)	$	(465	)