Earnings (Loss) Attributable to Tennant Company Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net Earnings (Loss) Attributable to Tennant Company	$ 3,559	$ 11,477	$ (2,989)	$ 31,244
Denominator:
Basic - Weighted Average Shares Outstanding	17,729,857	17,498,808	17,673,656	17,516,941
Effect of dilutive securities:
Share-based compensation plans	441,587	474,398	0	438,558
Diluted - Weighted Average Shares Outstanding	18,171,444	17,973,206	17,673,656	17,955,499
Basic Earnings (Loss) per Share	$ 0.20	$ 0.66	$ (0.17)	$ 1.78
Diluted (Loss) Earnings per Share	$ 0.20	$ 0.64	$ (0.17)	$ 1.74
Anti-dilutive securities excluded from earnings per share calculation	340,239	313,711	714,687	382,075