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		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Numerator:
Net income	$ 15.6	$ 21.5	$ 42.5	$ 57.0
Denominator:
Basic - weighted average shares outstanding (in shares)	18,515,851	18,554,136	18,495,640	18,519,523
Effect of dilutive securities:	176,065	317,081	217,697	350,375
Diluted - weighted average shares outstanding (in shares)	18,691,916	18,871,217	18,713,337	18,869,898
Basic earnings per share (in dollars per share)	$ 0.84	$ 1.16	$ 2.30	$ 3.08
Diluted earnings per share (in dollars per share)	$ 0.83	$ 1.14	$ 2.27	$ 3.02