Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Tennant Company Shareholders' Equity	Noncontrolling Interest
Beginning balance at Dec. 31, 2017	$ 298.5	$ 6.7	$ 15.1	$ 297.0	$ (22.3)	$ 296.5	$ 2.0
Balance (in shares) at Dec. 31, 2017		17,881,177
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	3.3	$ 0.0	0.0	3.3	0.0	3.3	0.0
Other Comprehensive (Loss) Income	5.1	$ 0.0	0.0	0.0	5.1	5.1	0.0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952 and 4,151 shares) (in shares)		29,263
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952 and 4,151 shares)	0.5	$ 0.0	0.5	0.0	0.0	0.5	0.0
Share-Based Compensation	2.7	0.0	2.7	0.0	0.0	2.7	0.0
Dividends paid ($0.22 and $0.21) per Common Share	(3.8)	0.0	0.0	(3.8)	0.0	(3.8)	0.0
Recognition of Noncontrolling Interests	(0.1)	0.0	0.0	0.0	0.0	0.0	(0.1)
Retained Earnings Adjustment	1.2	$ 0.0	0.0	1.2	0.0	1.2	0.0
Balance (in shares) at Mar. 31, 2018		17,910,440
Ending balance at Mar. 31, 2018	307.4	$ 6.7	18.3	297.7	(17.2)	305.5	1.9
Beginning balance at Dec. 31, 2018	$ 316.3	$ 6.8	28.5	316.3	(37.2)	314.4	1.9
Balance (in shares) at Dec. 31, 2018	18,125,201	18,125,201
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	$ 5.4	$ 0.0	0.0	5.4	0.0	5.4	0.0
Other Comprehensive (Loss) Income	(1.3)	$ 0.0	0.0	0.0	(1.3)	(1.3)	0.0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952 and 4,151 shares) (in shares)		35,338
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952 and 4,151 shares)	0.2	$ 0.0	0.2	0.0	0.0	0.2	0.0
Share-Based Compensation	3.3	0.0	3.3	0.0	0.0	3.3	0.0
Dividends paid ($0.22 and $0.21) per Common Share	(4.0)	0.0	0.0	(4.0)	0.0	(4.0)	0.0
Recognition of Noncontrolling Interests	$ 0.3	$ 0.0	0.0	0.0	0.0	0.0	0.3
Balance (in shares) at Mar. 31, 2019	18,160,539	18,160,539
Ending balance at Mar. 31, 2019	$ 320.2	$ 6.8	$ 32.0	$ 317.7	$ (38.5)	$ 318.0	$ 2.2