Note 15 - Subsequent Events	9 Months Ended
Sep. 30, 2022
Notes to Financial Statements
Subsequent Events [Text Block]	15. Subsequent Events In October 2022, Fuel Tech finalized a settlement agreement with a supplier related to an equipment component failure at a foreign customer location. The failure was previously recorded and remedied under the warranty provision of the contract. Per the agreement, Fuel Tech will receive a combination of cash, invoice forgiveness, and credit on future equipment purchases totaling approximately $245. Settlement amounts will be recorded during the fourth quarter of 2022.

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-URI https://asc.fasb.org/topic&trid=2122774

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=6842918&loc=SL6314017-165662

Name:	us-gaap_SubsequentEventsTextBlock
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:textBlockItemType
Balance Type:	na
Period Type:	duration