Business Segment Information - Segment Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jun. 30, 2020
Segment Reporting Information [Line Items]
Assets	$ 185,436	$ 146,671
Equity method investments	2,391	7,692
Expenditures	183	0
Deferred tax assets, net	0	10,604
Advanced Purification Technologies
Segment Reporting Information [Line Items]
Assets			$ 58,300
Operating Segments
Segment Reporting Information [Line Items]
Assets	88,400	92,393
Operating Segments | Refined Coal
Segment Reporting Information [Line Items]
Assets	4,884	11,516
Operating Segments | Advanced Purification Technologies
Segment Reporting Information [Line Items]
Assets	83,516	80,877
Long-lived assets	36,700	34,600
Expenditures	7,400	7,300
Corporate
Segment Reporting Information [Line Items]
Assets	$ 97,036	$ 54,278