Revenue Recognition (Tables)

12 Months Ended

Dec. 31, 2020

The following table disaggregates revenue by major sources for the years ended December 31:


Major Goods/Service Lines	2020		2019
Coal Mining	$	72,088	$	68,701
NAMining	42,392		42,823
Minerals Management	14,721		30,119
Unallocated Items	2,133		790
Eliminations	(2,902)		(1,443)
Total revenues	$	128,432	$	140,990

Timing of Revenue Recognition
Goods transferred at a point in time	$	68,073	$	66,102
Services transferred over time	60,359		74,888
Total revenues	$	128,432	$	140,990

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		Long-term asset		Contract liability (current)		Contract liability (long-term)
Balance at January 1, 2020	$	15,444	$	1,977	$	944	$	2,153
Balance at December 31, 2020	18,894		4,984		941		3,626
Increase (decrease)	$	3,450	$	3,007	$	(3)	$	1,473