Separate Financial Information of Guarantor Subsidiaries Statements of Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	$ 45.9	$ 33.5	$ (6.2)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(4.5)	(16.2)	28.3
Pension and retiree medical benefits	(0.5)	1.7	5.9
Cash flow hedge	4.6	1.3	(7.7)
Income Taxes:
Foreign currency translation adjustments	0.1	0.2	0.3
Pension and retiree medical benefits	0.1	(0.5)	(2.1)
Cash flow hedge	(1.1)	(1.4)	2.9
Total Other Comprehensive (Loss) Income, net of tax	(1.3)	(14.9)	27.6
Total Comprehensive Income Including Noncontrolling Interest	44.6	18.6	21.4
Comprehensive Income Attributable to Noncontrolling Interest	0.1	0.1	0.0
Comprehensive Income Attributable to Tennant Company	44.5	18.5	21.4
Parent Company
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	45.9	33.5	(6.2)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(4.5)	(16.2)	28.3
Pension and retiree medical benefits	(0.5)	1.7	5.9
Cash flow hedge	4.6	1.3	(7.7)
Income Taxes:
Foreign currency translation adjustments	0.1	0.2	0.3
Pension and retiree medical benefits	0.1	(0.5)	(2.1)
Cash flow hedge	(1.1)	(1.4)	2.9
Total Other Comprehensive (Loss) Income, net of tax	(1.3)	(14.9)	27.6
Total Comprehensive Income Including Noncontrolling Interest	44.6	18.6
Comprehensive Income Attributable to Noncontrolling Interest	0.1	0.1
Comprehensive Income Attributable to Tennant Company	44.5	18.5	21.4
Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	15.8	12.9	14.0
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	0.5	(1.0)	1.2
Pension and retiree medical benefits	0.0	0.0	0.0
Cash flow hedge	0.0	0.0	0.0
Income Taxes:
Foreign currency translation adjustments	0.0	0.0	0.0
Pension and retiree medical benefits	0.0	0.0	0.0
Cash flow hedge	0.0	0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	0.5	(1.0)	1.2
Total Comprehensive Income Including Noncontrolling Interest	16.3	11.9
Comprehensive Income Attributable to Noncontrolling Interest	0.0	0.0
Comprehensive Income Attributable to Tennant Company	16.3	11.9	15.2
Non-Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	8.5	19.0	19.9
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(4.9)	(21.4)	3.0
Pension and retiree medical benefits	(0.4)	1.2	0.6
Cash flow hedge	0.0	0.0	0.0
Income Taxes:
Foreign currency translation adjustments	0.1	0.2	0.3
Pension and retiree medical benefits	0.1	(0.2)	(0.1)
Cash flow hedge	0.0	0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	(5.1)	(20.2)	3.8
Total Comprehensive Income Including Noncontrolling Interest	3.4	(1.2)
Comprehensive Income Attributable to Noncontrolling Interest	0.1	0.1
Comprehensive Income Attributable to Tennant Company	3.3	(1.3)	23.7
Eliminations
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	(24.3)	(31.9)	(33.9)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	4.4	22.4	(4.2)
Pension and retiree medical benefits	0.4	(1.2)	(0.6)
Cash flow hedge	0.0	0.0	0.0
Income Taxes:
Foreign currency translation adjustments	(0.1)	(0.2)	(0.3)
Pension and retiree medical benefits	(0.1)	0.2	0.1
Cash flow hedge	0.0	0.0	0.0
Total Other Comprehensive (Loss) Income, net of tax	4.6	21.2	(5.0)
Total Comprehensive Income Including Noncontrolling Interest	(19.7)	(10.7)
Comprehensive Income Attributable to Noncontrolling Interest	(0.1)	(0.1)
Comprehensive Income Attributable to Tennant Company	$ (19.6)	$ (10.6)	$ (38.9)