Acquisitions (Details 3) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Sales
As reported	$ 279,295	$ 261,921	$ 270,791	$ 191,059	$ 211,746	$ 200,134	$ 216,828	$ 179,864	$ 1,003,066	$ 808,572	$ 811,799
Net Earnings (Loss) Attributable to Tennant Company
As reported	$ (3,206)	$ 3,559	$ (2,591)	$ (3,957)	$ 15,370	$ 11,477	$ 15,328	$ 4,439	$ (6,195)	$ 46,614	$ 32,088
Net Earnings (Loss) Attributable to Tennant Company per Diluted Share
As reported (in dollars per share)	$ (0.18)	$ 0.20	$ (0.15)	$ (0.22)	$ 0.85	$ 0.64	$ 0.85	$ 0.25	$ (0.35)	$ 2.59	$ 1.74
IP Cleaning S.p.A
Net Sales
Pro forma									$ 1,057,127	$ 1,013,710
As reported									174,444
Net Earnings (Loss) Attributable to Tennant Company
Pro forma									12,288	$ 30,412
As reported									$ 14,483
Net Earnings (Loss) Attributable to Tennant Company per Diluted Share
Pro forma (in dollars per share)									$ 0.68	$ 1.69