Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	$ 14.6	$ 14.8	$ 5.4	$ 9.7	$ 12.7	$ 3.3	$ 34.8	$ 25.8
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(12.6)			(3.1)			(13.5)	(14.2)
Pension and retiree medical benefits	0.0			0.0			0.0	0.1
Cash flow hedge	1.7			0.0			4.3	(1.4)
Income Taxes:
Foreign currency translation adjustments	0.1			0.3			0.1	0.6
Pension and retiree medical benefits	0.0			0.0			0.0	(0.2)
Cash flow hedge	(0.4)			0.0			(1.0)	(0.8)
Total Other Comprehensive (Loss) Income, net of tax	(11.2)			(2.8)			(10.1)	(15.9)
Total Comprehensive Income Including Noncontrolling Interest	3.4			6.9			24.7	9.9
Comprehensive Income Attributable to Noncontrolling Interest	0.0			0.0			0.0	0.1
Comprehensive Income Attributable to Tennant Company	3.4			6.9			24.7	9.8
Eliminations
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	(7.3)			(5.5)			(16.2)	(22.5)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	23.8			3.5			24.7	20.4
Pension and retiree medical benefits	0.0			0.0			0.0	0.0
Cash flow hedge	0.0			0.0			0.0	0.0
Income Taxes:
Foreign currency translation adjustments	1.1			(0.3)			0.1	(0.5)
Pension and retiree medical benefits	0.0			0.0			0.0	0.0
Cash flow hedge	0.0			0.0			0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	24.9			3.2			24.8	19.9
Total Comprehensive Income Including Noncontrolling Interest	17.6			(2.3)			8.6	(2.6)
Comprehensive Income Attributable to Noncontrolling Interest								(0.1)
Comprehensive Income Attributable to Tennant Company	17.6			(2.3)			8.6	(2.5)
Parent
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	14.6			9.7			34.8	25.8
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(12.6)			(3.1)			(13.5)	(14.2)
Pension and retiree medical benefits	0.0			0.0			0.0	0.1
Cash flow hedge	1.7			0.0			4.3	(1.4)
Income Taxes:
Foreign currency translation adjustments	0.1			0.3			0.1	0.6
Pension and retiree medical benefits	0.0			0.0			0.0	(0.2)
Cash flow hedge	(0.4)			0.0			(1.0)	(0.8)
Total Other Comprehensive (Loss) Income, net of tax	(11.2)			(2.8)			(10.1)	(15.9)
Total Comprehensive Income Including Noncontrolling Interest	3.4			6.9			24.7	9.9
Comprehensive Income Attributable to Noncontrolling Interest								0.1
Comprehensive Income Attributable to Tennant Company	3.4			6.9			24.7	9.8
Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	4.5			3.9			12.6	11.1
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(9.9)			0.2			(10.1)	(0.3)
Pension and retiree medical benefits	0.0			0.0			0.0	0.0
Cash flow hedge	0.0			0.0			0.0	0.0
Income Taxes:
Foreign currency translation adjustments	0.0			0.0			0.0	0.0
Pension and retiree medical benefits	0.0			0.0			0.0	0.0
Cash flow hedge	0.0			0.0			0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	(9.9)			0.2			(10.1)	(0.3)
Total Comprehensive Income Including Noncontrolling Interest	(5.4)			4.1			2.5	10.8
Comprehensive Income Attributable to Noncontrolling Interest								0.0
Comprehensive Income Attributable to Tennant Company	(5.4)			4.1			2.5	10.8
Non-Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	2.8			1.6			3.6	11.4
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(13.9)			(3.7)			(14.6)	(20.1)
Pension and retiree medical benefits	0.0			0.0			0.0	0.0
Cash flow hedge	0.0			0.0			0.0	0.0
Income Taxes:
Foreign currency translation adjustments	(1.1)			0.3			(0.1)	0.5
Pension and retiree medical benefits	0.0			0.0			0.0	0.0
Cash flow hedge	0.0			0.0			0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	(15.0)			(3.4)			(14.7)	(19.6)
Total Comprehensive Income Including Noncontrolling Interest	(12.2)			(1.8)			(11.1)	(8.2)
Comprehensive Income Attributable to Noncontrolling Interest								0.1
Comprehensive Income Attributable to Tennant Company	$ (12.2)			$ (1.8)			$ (11.1)	$ (8.3)