Note 16 - Income Attributable to Tennant Company 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, 2022	Mar. 31, 2021
Net income attributable to Tennant Company	$ 10.3	$ 25.7
Basic - weighted average shares outstanding (in shares)	18,463,419	18,456,079
Effect of dilutive securities: (in shares)	336,313	375,344
Diluted - weighted average shares outstanding (in shares)	18,799,732	18,831,423
Basic earnings per share attributable to Tennant Company (in dollars per share)	$ 0.56	$ 1.39
Diluted earnings per share attributable to Tennant Company (in dollars per share)	$ 0.55	$ 1.37