Earnings Per Share - Computations of Basic and Diluted Earnings (Loss) Attributable to Tennant Company Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Numerator:
Net income	$ 24.3	$ 10.3
Denominator:
Basic - weighted average shares outstanding (in shares)	18,449,430	18,463,419
Effect of dilutive securities:	232,838	336,313
Diluted - weighted average shares outstanding (in shares)	18,682,268	18,799,732
Basic earnings per share (in dollars per share)	$ 1.32	$ 0.56
Diluted earnings per share (in dollars per share)	$ 1.30	$ 0.55