Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	$ 9,709	$ 3,596	$ 25,775	$ (3,017)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(3,110)	9,033	(14,202)	25,073
Pension and retiree medical benefits	12	379	105	541
Cash flow hedge	(28)	(1,732)	(1,367)	(6,311)
Income Taxes:
Foreign currency translation adjustments	280	0	524	0
Pension and retiree medical benefits	(2)	(138)	(156)	(160)
Cash flow hedge	6	646	(814)	2,354
Total Other Comprehensive (Loss) Income, net of tax	(2,842)	8,188	(15,910)	21,497
Total Comprehensive Income Including Noncontrolling Interest	6,867	11,784	9,865	18,480
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	33	37	81	(28)
Comprehensive Income Attributable to Tennant Company	6,834	11,747	9,784	18,508
Eliminations
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	(5,516)	3,131	(22,520)	3,305
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	3,436	(9,510)	20,365	(2,023)
Pension and retiree medical benefits	0	(10)	(19)	(151)
Cash flow hedge	0	0	0	0
Income Taxes:
Foreign currency translation adjustments	(280)	0	(524)	0
Pension and retiree medical benefits	0	0	0	15
Cash flow hedge	0	0	0	0
Total Other Comprehensive (Loss) Income, net of tax	3,156	(9,520)	19,822	(2,159)
Total Comprehensive Income Including Noncontrolling Interest	(2,360)	(6,389)	(2,698)	1,146
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	(33)	(37)	(81)	28
Comprehensive Income Attributable to Tennant Company	(2,327)	(6,352)	(2,617)	1,118
Parent
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	9,709	3,596	25,775	(3,017)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(3,110)	9,033	(14,202)	25,073
Pension and retiree medical benefits	12	379	105	541
Cash flow hedge	(28)	(1,732)	(1,367)	(6,311)
Income Taxes:
Foreign currency translation adjustments	280	0	524	0
Pension and retiree medical benefits	(2)	(138)	(156)	(160)
Cash flow hedge	6	646	(814)	2,354
Total Other Comprehensive (Loss) Income, net of tax	(2,842)	8,188	(15,910)	21,497
Total Comprehensive Income Including Noncontrolling Interest	6,867	11,784	9,865	18,480
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	33	37	81	(28)
Comprehensive Income Attributable to Tennant Company	6,834	11,747	9,784	18,508
Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	3,911	3,497	11,137	10,684
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	228	289	(262)	693
Pension and retiree medical benefits	0	0	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	0	0
Cash flow hedge	0	0	0	0
Total Other Comprehensive (Loss) Income, net of tax	228	289	(262)	693
Total Comprehensive Income Including Noncontrolling Interest	4,139	3,786	10,875	11,377
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	0	0	0	0
Comprehensive Income Attributable to Tennant Company	4,139	3,786	10,875	11,377
Non-Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net Earnings (Loss) Including Noncontrolling Interest	1,605	(6,628)	11,383	(13,989)
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(3,664)	9,221	(20,103)	1,330
Pension and retiree medical benefits	0	10	19	151
Cash flow hedge	0	0	0	0
Income Taxes:
Foreign currency translation adjustments	280	0	524	0
Pension and retiree medical benefits	0	0	0	(15)
Cash flow hedge	0	0	0	0
Total Other Comprehensive (Loss) Income, net of tax	(3,384)	9,231	(19,560)	1,466
Total Comprehensive Income Including Noncontrolling Interest	(1,779)	2,603	(8,177)	(12,523)
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	33	37	81	(28)
Comprehensive Income Attributable to Tennant Company	$ (1,812)	$ 2,566	$ (8,258)	$ (12,495)