Organization and Significant Accounting Policies - Additional Information (Details)		3 Months Ended								12 Months Ended
	Oct. 01, 2018 USD ($)	Dec. 31, 2019 USD ($) unit shares	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) unit shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 shares
Revenues		$ 4,912,000	$ 6,452,000	$ 8,948,000	$ 10,155,000	$ 15,827,000	$ 16,070,000	$ 11,847,000	$ 12,791,000	$ 30,467,000	$ 56,535,000	$ 45,166,000
Percentage of net income from International revenues										15.00%	22.00%	35.00%
Restricted cash included in current assets		2,080,000				6,020,000				$ 2,080,000	$ 6,020,000
Restricted cash included in long-term assets		507,000				0				507,000	0
Bankers acceptance		43,000				997,000				43,000	997,000
Foreign currency translation		0								$ 370,000	0	$ 0
Number of reporting units | unit										2
Impairment of goodwill										$ 0	0	0
Goodwill		2,116,000				2,116,000				2,116,000	2,116,000
Impairment charges										127,000
Intangible assets impairment										127,000	317,000	2,965,000
Intangible assets abandonment and building impairment										127,000	317,000	2,965,000
Patents		$ 906,000				$ 1,164,000				906,000	1,164,000
Amortization of intangible assets										186,000	193,000	215,000
Depreciation										$ 810,000	$ 654,000	$ 1,312,000
Number of units with APC technology installed | unit		1,100								1,100
Options outstanding (in shares) | shares		747,500				932,500				747,500	932,500	1,116,750	1,039,750
Antidilutive equity awards (In shares) | shares										728,000	620,000	168,000
Treasury shares withheld (in shares) | shares										140,784	11,215
Treasury shares withheld										$ 128,000	$ 12,000	$ 258,000
Capitalized Third-party Costs
Patents		$ 56,000				$ 59,000				$ 56,000	$ 59,000
Minimum
Warranty period (in years)										1 year
Maximum
Warranty period (in years)										2 years
Antidilutive
Options outstanding (in shares) | shares		913,000				757,000				913,000	757,000	2,210,000
FUEL CHEM Segment
Revenues										$ 16,385,000	$ 18,118,000	$ 17,358,000
Impairment of goodwill	$ 0
Goodwill						$ 2,116,000					$ 2,116,000
APC Technology Segment
Goodwill		$ 0								$ 0
APC Technology Segment | Minimum
Duration of contracts		6 months								6 months
APC Technology Segment | Maximum
Duration of contracts		18 months								18 months
Customer One | Sales Revenue, Services, Net
Concentration risk percentage										19.00%	27.00%	10.00%
Customer Two | Sales Revenue, Services, Net
Concentration risk percentage										11.00%	13.00%
Project and Non-Project
Unbilled contracts receivable		$ 1,857,000				$ 5,540,000				$ 1,857,000	$ 5,540,000
2014 Long-Term Incentive Plan
Number of shares reserved for future issuance (in shares) | shares		5,600,676								5,600,676
Incentive Plan
Number of shares reserved for future issuance | shares		2,231,382								2,231,382
Chinese Subsidiary
Restricted cash on hand		$ 1,417,000								$ 1,417,000
Italian Subsidiary
Cash		1,695,000								1,695,000
Chilean Subsidiary
Cash		0								0
Cash Collateral Security Agreement | Standby Letters of Credit
Restricted cash		2,587								2,587
Restricted cash included in current assets		2,000								2,000
Restricted cash included in long-term assets		$ 1,000								1,000
Foreign
Revenues										$ 4,585,000	$ 12,648,000	$ 15,656,000