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, 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
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, 1,560, 4,151, 3,360, and 1,327 shares) (in shares)		35,338
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 1,560, 4,151, 3,360, and 1,327 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, $0.22, $0.21,$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
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	20.2
Balance (in shares) at Jun. 30, 2019		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, 1,560, 4,151, 3,360, and 1,327 shares) (in shares)		31,947
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 1,560, 4,151, 3,360, and 1,327 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, $0.22, $0.21,$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)
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
Ending balance at Jun. 30, 2019	335.2	$ 6.8	34.5	328.5	(36.1)	333.7	1.5
Increase (Decrease) in Stockholders' Equity
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	0.0	0.0	0.5	0.0	0.0	0.5	(0.5)
Beginning balance at Dec. 31, 2019	$ 361.3	$ 6.9	45.5	346.0	(38.5)	359.9	1.4
Balance (in shares) at Dec. 31, 2019	18,336,010	18,336,010
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	$ 5.2	$ 0.0	0.0	5.2	0.0	5.2	0.0
Other Comprehensive (Loss) Income	(7.6)	$ 0.0	0.0	0.0	(7.6)	(7.6)	0.0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 1,560, 4,151, 3,360, and 1,327 shares) (in shares)		98,805
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 1,560, 4,151, 3,360, and 1,327 shares)	1.1	$ 0.0	1.1	0.0	0.0	1.1	0.0
Share-Based Compensation	2.8	0.0	2.8	0.0	0.0	2.8	0.0
Dividends paid ($0.22, $0.22, $0.22, $0.21,$0.21, and $0.21) per Common Share	(4.0)	0.0	0.0	(4.0)	0.0	(4.0)	0.0
Other	(0.1)	$ 0.0	0.0	(0.1)	0.0	(0.1)	0.0
Balance (in shares) at Mar. 31, 2020		18,434,815
Ending balance at Mar. 31, 2020	358.7	$ 6.9	49.4	347.1	(46.1)	357.3	1.4
Beginning balance at Dec. 31, 2019	$ 361.3	$ 6.9	45.5	346.0	(38.5)	359.9	1.4
Balance (in shares) at Dec. 31, 2019	18,336,010	18,336,010
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	$ 19.5
Balance (in shares) at Jun. 30, 2020	18,455,462	18,455,462
Ending balance at Jun. 30, 2020	$ 373.1	$ 6.9	49.4	357.4	(42.0)	371.7	1.4
Beginning balance at Mar. 31, 2020	358.7	$ 6.9	49.4	347.1	(46.1)	357.3	1.4
Balance (in shares) at Mar. 31, 2020		18,434,815
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	14.3	$ 0.0	0.0	14.3	0.0	14.3	0.0
Other Comprehensive (Loss) Income	4.1	$ 0.0	0.0	0.0	4.1	4.1	0.0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 1,560, 4,151, 3,360, and 1,327 shares) (in shares)		20,647
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (6,952, 3,310, 1,560, 4,151, 3,360, and 1,327 shares)	0.0	$ 0.0	0.0	0.0	0.0	0.0	0.0
Dividends paid ($0.22, $0.22, $0.22, $0.21,$0.21, and $0.21) per Common Share	$ (4.0)	$ 0.0	0.0	(4.0)	0.0	(4.0)	0.0
Balance (in shares) at Jun. 30, 2020	18,455,462	18,455,462
Ending balance at Jun. 30, 2020	$ 373.1	$ 6.9	$ 49.4	$ 357.4	$ (42.0)	$ 371.7	$ 1.4