Note 16 - 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		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Net income	$ 16.6	$ 9.8	$ 26.9	$ 35.5
Basic - weighted average shares outstanding (in shares)	18,507,073	18,547,276	18,485,367	18,501,930
Effect of dilutive securities: (in shares)	176,725	384,427	250,546	377,686
Diluted - weighted average shares outstanding (in shares)	18,683,798	18,931,703	18,735,913	18,879,616
Basic (in dollars per share)	$ 0.90	$ 0.53	$ 1.46	$ 1.92
Diluted earnings per share (in dollars per share)	$ 0.89	$ 0.51	$ 1.44	$ 1.88