Revenue Recognition - Revenues Disaggregated by Product Technology (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total Revenues	$ 30,467	$ 56,535	$ 45,166
Air Pollution Control
Disaggregation of Revenue [Line Items]
Total Revenues	14,082	38,417	27,808
Air Pollution Control | Technology solutions
Disaggregation of Revenue [Line Items]
Total Revenues	10,640	35,176	24,422
Air Pollution Control | Spare parts
Disaggregation of Revenue [Line Items]
Total Revenues	1,031	1,083	1,022
Air Pollution Control | Ancillary revenue
Disaggregation of Revenue [Line Items]
Total Revenues	2,411	2,158	2,364
FUEL CHEM | Technology solutions
Disaggregation of Revenue [Line Items]
Total Revenues	$ 16,385	$ 18,118	$ 17,358