Revenue (Tables)

6 Months Ended

Jun. 30, 2019

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,
	2019		2018		2019		2018
Products transferred at a point in time	$	5,153	$	4,255	$	10,567	$	9,324
Products and services transferred over time	3,795		7,592		8,536		15,314
Total Revenues	$	8,948	$	11,847	$	19,103	$	24,638

The following table presents our revenues disaggregated by product technology:

	Three Months Ended   June 30,				Six Months Ended   June 30,
	2019		2018		2019		2018
Air Pollution Control
Technology solutions	$	3,795	$	7,592	$	8,536	$	15,314
Spare parts	384		229		533		529
Ancillary revenue	624		586		1,523		1,147
Total Air Pollution Control Technology revenues	4,803		8,407		10,592		16,990
FUEL CHEM
FUEL CHEM technology solutions	4,145		3,440		8,511		7,648
Total Revenues	$	8,948	$	11,847	$	19,103	$	24,638

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,
	2019		2018		2019		2018
United States	$	7,562	$	8,830	$	16,377	$	19,072
Foreign Revenues
South America	17		354		192		626
Europe	668		1,562		1,285		3,028
Asia	701		1,101		1,249		1,912
Total Foreign Revenues	1,386		3,017		2,726		5,566
Total Revenues	$	8,948	$	11,847	$	19,103	$	24,638

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

The components of accounts receivable are as follows:

	As of
	June 30, 2019			December 31, 2018
Trade receivables	$	11,403		$	14,261
Unbilled receivables	2,338			5,540
Insurance proceeds receivable (Note 14)	1,978			—
Other short-term receivables	124			9
Allowance for doubtful accounts	(1,216		)	(1,411		)
Total accounts receivable	$	14,627		$	18,399