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, 3,310, 4,151, and 3,360 shares) (in shares)		29,263
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 4,151, and 3,360 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, $0.22, $0.21, 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, 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)	16.1
Purchase of Noncontrolling Owner Interest	0.0
Balance (in shares) at Jun. 30, 2018		18,073,713
Ending balance at Jun. 30, 2018	302.2	$ 6.8	22.3	306.6	(35.4)	300.3	1.9
Beginning balance at Mar. 31, 2018	307.4	$ 6.7	18.3	297.7	(17.2)	305.5	1.9
Balance (in shares) at Mar. 31, 2018		17,910,440
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	12.7	$ 0.0	0.0	12.7	0.0	12.7	0.0
Other Comprehensive (Loss) Income	(18.2)	$ 0.0	0.0	0.0	(18.2)	(18.2)	0.0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 4,151, and 3,360 shares) (in shares)		163,273
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 4,151, and 3,360 shares)	2.7	$ 0.1	2.6	0.0	0.0	2.7	0.0
Share-Based Compensation	1.4	0.0	1.4	0.0	0.0	1.4	0.0
Dividends paid ($0.22, $0.22, $0.21, and $0.21) per Common Share	(3.8)	$ 0.0	0.0	(3.8)	0.0	(3.8)	0.0
Balance (in shares) at Jun. 30, 2018		18,073,713
Ending balance at Jun. 30, 2018	302.2	$ 6.8	22.3	306.6	(35.4)	300.3	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, 3,310, 4,151, and 3,360 shares) (in shares)		35,338
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 4,151, and 3,360 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, $0.22, $0.21, 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
Ending balance at Mar. 31, 2019	320.2	$ 6.8	32.0	317.7	(38.5)	318.0	2.2
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)	$ 20.2
Purchase of Noncontrolling Owner Interest	$ (0.5)
Balance (in shares) at Jun. 30, 2019	18,192,486	18,192,486
Ending balance at Jun. 30, 2019	$ 335.2	$ 6.8	34.5	328.5	(36.1)	333.7	1.5
Beginning balance at Mar. 31, 2019	320.2	$ 6.8	32.0	317.7	(38.5)	318.0	2.2
Balance (in shares) at Mar. 31, 2019		18,160,539
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	14.8	$ 0.0	0.0	14.8	0.0	14.8	0.0
Other Comprehensive (Loss) Income	2.4	$ 0.0	0.0	0.0	2.4	2.4	0.0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 4,151, and 3,360 shares) (in shares)		31,947
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 4,151, and 3,360 shares)	0.3	$ 0.0	0.3	0.0	0.0	0.3	0.0
Share-Based Compensation	1.7	0.0	1.7	0.0	0.0	1.7	0.0
Dividends paid ($0.22, $0.22, $0.21, 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)
Purchase of Noncontrolling Owner Interest	0.0	0.0	0.5	0.0	0.0	0.5	(0.5)
Other	$ 0.1	$ 0.0	0.0	0.0	0.0	0.0	0.1
Balance (in shares) at Jun. 30, 2019	18,192,486	18,192,486
Ending balance at Jun. 30, 2019	$ 335.2	$ 6.8	$ 34.5	$ 328.5	$ (36.1)	$ 333.7	$ 1.5