Separate Financial Information of Guarantor Subsidiaries Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	$ 33,538	$ (6,205)	$ 46,614
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(16,221)	28,356	109
Pension and retiree medical benefits	1,745	5,868	(2,248)
Cash flow hedge	1,341	(7,731)	(305)
Income Taxes:
Foreign currency translation adjustments	168	310	32
Pension and retiree medical benefits	(467)	(2,087)	504
Cash flow hedge	(1,437)	2,884	114
Total Other Comprehensive (Loss) Income, net of tax	(14,871)	27,600	(1,794)
Total Comprehensive Income Including Noncontrolling Interest	18,667	21,395	44,820
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	126	(10)	0
Comprehensive Income Attributable to Tennant Company	18,541	21,405	44,820
Parent Company
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	33,538	(6,205)	46,614
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(16,221)	28,356	109
Pension and retiree medical benefits	1,745	5,868	(2,248)
Cash flow hedge	1,341	(7,731)	(305)
Income Taxes:
Foreign currency translation adjustments	168	310	32
Pension and retiree medical benefits	(467)	(2,087)	504
Cash flow hedge	(1,437)	2,884	114
Total Other Comprehensive (Loss) Income, net of tax	(14,871)	27,600	(1,794)
Total Comprehensive Income Including Noncontrolling Interest	18,667	21,395
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	126	(10)
Comprehensive Income Attributable to Tennant Company	18,541	21,405	44,820
Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	12,840	14,024	15,622
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(961)	1,215	270
Pension and retiree medical benefits	0	0	0
Cash flow hedge	0	0	0
Income Taxes:
Foreign currency translation adjustments	0	0	0
Pension and retiree medical benefits	0	0	0
Cash flow hedge	0	0	0
Total Other Comprehensive (Loss) Income, net of tax	(961)	1,215	270
Total Comprehensive Income Including Noncontrolling Interest	11,879	15,239
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	0	0
Comprehensive Income Attributable to Tennant Company	11,879	15,239	15,892
Non-Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	19,010	19,977	8,842
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(21,422)	2,960	3,534
Pension and retiree medical benefits	1,197	538	(1,691)
Cash flow hedge	0	0	0
Income Taxes:
Foreign currency translation adjustments	168	310	32
Pension and retiree medical benefits	(205)	(99)	296
Cash flow hedge	0	0	0
Total Other Comprehensive (Loss) Income, net of tax	(20,262)	3,709	2,171
Total Comprehensive Income Including Noncontrolling Interest	(1,252)	23,686
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	126	(10)
Comprehensive Income Attributable to Tennant Company	(1,378)	23,696	11,013
Eliminations
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	(31,850)	(34,001)	(24,464)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	22,383	(4,175)	(3,804)
Pension and retiree medical benefits	(1,197)	(538)	1,691
Cash flow hedge	0	0	0
Income Taxes:
Foreign currency translation adjustments	(168)	(310)	(32)
Pension and retiree medical benefits	205	99	(296)
Cash flow hedge	0	0	0
Total Other Comprehensive (Loss) Income, net of tax	21,223	(4,924)	(2,441)
Total Comprehensive Income Including Noncontrolling Interest	(10,627)	(38,925)
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	(126)	10
Comprehensive Income Attributable to Tennant Company	$ (10,501)	$ (38,935)	$ (26,905)