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, 2016	$ 278.5	$ 6.6	$ 3.6	$ 318.2	$ (49.9)	$ 278.5	$ 0.0
Balance (in shares) at Dec. 31, 2016		17,688,350
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	(6.2)	$ 0.0	0.0	(6.2)	0.0	(6.2)	0.0
Other Comprehensive (Loss) Income	27.6	$ 0.0	0.0	0.0	27.6	27.6	0.0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares) (in shares)		192,827
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares)	5.7	$ 0.1	5.6	0.0	0.0	5.7	0.0
Share-Based Compensation	5.9	0.0	5.9	0.0	0.0	5.9	0.0
Dividends paid ($0.81, $0.84 and $0.85) per Common Share	(15.0)	0.0	0.0	(15.0)	0.0	(15.0)	0.0
Tax Benefit on Stock Plans	2.0	$ 0.0	0.0	0.0	0.0	0.0	2.0
Balance (in shares) at Dec. 31, 2017		17,881,177
Ending balance at Dec. 31, 2017	298.5	$ 6.7	15.1	297.0	(22.3)	296.5	2.0
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	33.5	0.0	0.0	33.4	0.0	33.4	0.1
Other Comprehensive (Loss) Income	(14.9)	$ 0.0	0.0	0.0	(14.9)	(14.9)	0.0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares) (in shares)		244,024
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares)	5.2	$ 0.1	5.1	0.0	0.0	5.2	0.0
Share-Based Compensation	8.3	0.0	8.3	0.0	0.0	8.3	0.0
Dividends paid ($0.81, $0.84 and $0.85) per Common Share	(15.3)	0.0	0.0	(15.3)	0.0	(15.3)	0.0
Recognition of Noncontrolling Interests	(0.2)	0.0	0.0	0.0	0.0	0.0	(0.2)
Purchase of Noncontrolling Shareholder Interest	$ (1.2)	$ 0.0	0.0	(1.2)	0.0	(1.2)	0.0
Balance (in shares) at Dec. 31, 2018	18,125,201	18,125,201
Ending balance at Dec. 31, 2018	$ 316.3	$ 6.8	28.5	316.3	(37.2)	314.4	1.9
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	45.9	0.0	0.0	45.8	0.0	45.8	0.1
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 (23,113, 16,990 and 9,598 shares) (in shares)		210,809
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares)	5.2	$ 0.1	5.1	0.0	0.0	5.2	0.0
Share-Based Compensation	11.4	0.0	11.4	0.0	0.0	11.4	0.0
Dividends paid ($0.81, $0.84 and $0.85) per Common Share	(16.0)	0.0	0.0	(16.0)	0.0	(16.0)	0.0
Recognition of Noncontrolling Interests	0.0	0.0	0.5	0.0	0.0	0.5	(0.5)
Other	$ (0.2)	$ 0.0	0.0	(0.1)	0.0	(0.1)	(0.1)
Balance (in shares) at Dec. 31, 2019	18,336,010	18,336,010
Ending balance at Dec. 31, 2019	$ 361.3	$ 6.9	$ 45.5	$ 346.0	$ (38.5)	$ 359.9	$ 1.4