Earnings (Loss) Attributable to Tennant Company Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net Earnings (Loss) Attributable to Tennant Company	$ 9,676	$ 3,559	$ 25,694	$ (2,989)
Denominator:
Basic - Weighted Average Shares Outstanding	17,998,917	17,729,857	17,911,880	17,673,656
Effect of dilutive securities:
Share-based compensation plans	440,704	441,587	432,933	0
Diluted - Weighted Average Shares Outstanding	18,439,621	18,171,444	18,344,813	17,673,656
Basic Earnings (Loss) per Share	$ 0.54	$ 0.20	$ 1.43	$ (0.17)
Diluted Earnings (Loss) per Share	$ 0.52	$ 0.20	$ 1.40	$ (0.17)
Anti-dilutive securities excluded from earnings per share calculation	139,106	340,239	214,605	714,687