Income Attributable to Tennant Company Per Share - Schedule of Computations of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Numerator:
Net income	$ 0.2	$ 13.1
Denominator:
Basic - weighted average shares outstanding (in shares)	17,558,556	18,702,438
Effect of dilutive securities (in shares)	246,047	257,569
Diluted - weighted average shares outstanding (in shares)	17,804,603	18,960,007
Basic earnings per share (in dollars per share)	$ 0.01	$ 0.70
Diluted earnings per share (in dollars per share)	$ 0.01	$ 0.69