Revenue (Tables)

6 Months Ended

Jun. 30, 2020

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The following table presents the timing of our revenue recognition:

	Three Months Ended   June 30,				Six Months Ended   June 30,
	2020		2019		2020		2019
Products transferred at a point in time	$	2,932	$	5,153	$	5,981	$	10,567
Products and services transferred over time	1,469		3,795		2,198		8,536
Total Revenues	$	4,401	$	8,948	$	8,179	$	19,103

The following table presents our revenues disaggregated by product technology:

	Three Months Ended   June 30,				Six Months Ended   June 30,
	2020		2019		2020		2019
Air Pollution Control
Technology solutions	$	1,469	$	3,795	$	2,198	$	8,536
Spare parts	214		384		413		533
Ancillary revenue	254		624		522		1,523
Total Air Pollution Control Technology revenues	1,937		4,803		3,133		10,592
FUEL CHEM
FUEL CHEM technology solutions	2,464		4,145		5,046		8,511
Total Revenues	$	4,401	$	8,948	$	8,179	$	19,103

Revenue Disaggregated by Geography

The following table presents our revenues disaggregated by geography, based on the billing addresses of our customers:

	Three Months Ended   June 30,				Six Months Ended   June 30,
	2020		2019		2020		2019
United States	$	3,310	$	7,562	$	6,407	$	16,377
Foreign Revenues
Latin America	59		17		205		192
Europe	197		668		590		1,285
Asia	835		701		977		1,249
Total Foreign Revenues	1,091		1,386		1,772		2,726
Total Revenues	$	4,401	$	8,948	$	8,179	$	19,103

Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]

The components of accounts receivable are as follows:

	As of
	June 30, 2020			December 31, 2019
Trade receivables	$	4,592		$	6,425
Unbilled receivables	1,763			1,857
Other short-term receivables	19			7
Allowance for doubtful accounts	(716		)	(1,816		)
Total accounts receivable	$	5,658		$	6,473