Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	$ 5.2	$ 5.4
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(11.3)	(2.3)
Pension and retiree medical benefits		0.0
Cash flow hedge	4.8	1.4
Income Taxes:
Foreign currency translation adjustments	0.0	(0.1)
Pension and retiree medical benefits		0.0
Cash flow hedge	(1.1)	(0.3)
Total Other Comprehensive (Loss) Income, net of tax	(7.6)	(1.3)
Total Comprehensive Income Including Noncontrolling Interest	(2.4)	4.1
Comprehensive Income Attributable to Tennant Company	(2.4)	4.1
Eliminations
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	(0.1)	(2.1)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	20.3	22.6
Pension and retiree medical benefits		(1.2)
Cash flow hedge	0.0	0.0
Income Taxes:
Foreign currency translation adjustments	0.0	(0.1)
Pension and retiree medical benefits		0.3
Cash flow hedge	0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	20.3	21.6
Total Comprehensive Income Including Noncontrolling Interest	20.2	19.5
Comprehensive Income Attributable to Tennant Company	20.2	19.5
Parent
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	5.2	5.4
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(11.3)	(2.3)
Pension and retiree medical benefits		0.0
Cash flow hedge	4.8	1.4
Income Taxes:
Foreign currency translation adjustments	0.0	(0.1)
Pension and retiree medical benefits		0.0
Cash flow hedge	(1.1)	(0.3)
Total Other Comprehensive (Loss) Income, net of tax	(7.6)	(1.3)
Total Comprehensive Income Including Noncontrolling Interest	(2.4)	4.1
Comprehensive Income Attributable to Tennant Company	(2.4)	4.1
Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	3.7	4.1
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(0.3)	0.0
Pension and retiree medical benefits		0.0
Cash flow hedge	0.0	0.0
Income Taxes:
Foreign currency translation adjustments	0.0	0.0
Pension and retiree medical benefits		0.0
Cash flow hedge	0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	(0.3)	0.0
Total Comprehensive Income Including Noncontrolling Interest	3.4	4.1
Comprehensive Income Attributable to Tennant Company	3.4	4.1
Non-Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings Including Noncontrolling Interest	(3.6)	(2.0)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(20.0)	(22.6)
Pension and retiree medical benefits		1.2
Cash flow hedge	0.0	0.0
Income Taxes:
Foreign currency translation adjustments	0.0	0.1
Pension and retiree medical benefits		(0.3)
Cash flow hedge	0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	(20.0)	(21.6)
Total Comprehensive Income Including Noncontrolling Interest	(23.6)	(23.6)
Comprehensive Income Attributable to Tennant Company	$ (23.6)	$ (23.6)