Revenue - Revenues Disaggregated by Product Technology (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total Revenues	$ 11,847,000	$ 9,741,000	$ 24,638,000	$ 18,232,000
Air Pollution Control
Disaggregation of Revenue [Line Items]
Total Revenues	8,407,000	5,545,000	16,990,000	9,547,000
Air Pollution Control | Technology solutions
Disaggregation of Revenue [Line Items]
Total Revenues	7,592,000	4,754,000	15,314,000	8,102,000
Air Pollution Control | Spare parts
Disaggregation of Revenue [Line Items]
Total Revenues	229,000	267,000	529,000	536,000
Air Pollution Control | Ancillary revenue
Disaggregation of Revenue [Line Items]
Total Revenues	586,000	524,000	1,147,000	909,000
FUEL CHEM
Disaggregation of Revenue [Line Items]
Total Revenues	3,440,000	4,196,000	7,648,000	8,685,000
FUEL CHEM | Technology solutions
Disaggregation of Revenue [Line Items]
Total Revenues	$ 3,440,000	$ 4,196,000	$ 7,648,000	$ 8,685,000