Earnings Attributable to Tennant Company Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net Earnings Attributable to Tennant Company	$ 11.7	$ 14.6	$ 31.2	$ 34.8
Denominator:
Basic - Weighted Average Shares Outstanding	18,371,883	18,134,909	18,335,430	18,086,962
Effect of dilutive securities:
Share-based compensation plans	276,445	353,039	288,537	315,967
Diluted - Weighted Average Shares Outstanding	18,648,328	18,487,948	18,623,967	18,402,929
Basic Earnings (Loss) per Share	$ 0.64	$ 0.81	$ 1.70	$ 1.93
Diluted Earnings (Loss) per Share	$ 0.63	$ 0.79	$ 1.68	$ 1.89
Anti-dilutive securities excluded from earnings per share calculation	578,858	485,853	620,605	687,972