Separate Financial Information of Guarantor Subsidiaries Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net (Loss) Earnings Including Noncontrolling Interest	$ (6,205)	$ 46,614	$ 32,088
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	28,356	109	(12,520)
Pension and retiree medical benefits	5,868	(2,248)	4,121
Cash flow hedge	(7,731)	(305)	164
Income Taxes:
Foreign currency translation adjustments	310	32	25
Pension and retiree medical benefits	(2,087)	504	(1,265)
Cash flow hedge	2,884	114	(61)
Total Other Comprehensive (Loss) Income, net of tax	27,600	(1,794)	(9,536)
Total Comprehensive Income Including Noncontrolling Interest	21,395	44,820	22,552
Comprehensive Loss Attributable to Noncontrolling Interest	(10)	0	0
Comprehensive Income Attributable to Tennant Company	21,405	44,820	22,552
Parent Company
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net (Loss) Earnings Including Noncontrolling Interest	(6,205)	46,614	32,088
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	28,356	109	(12,520)
Pension and retiree medical benefits	5,868	(2,248)	4,121
Cash flow hedge	(7,731)	(305)	164
Income Taxes:
Foreign currency translation adjustments	310	32	25
Pension and retiree medical benefits	(2,087)	504	(1,265)
Cash flow hedge	2,884	114	(61)
Total Other Comprehensive (Loss) Income, net of tax	27,600	(1,794)	(9,536)
Total Comprehensive Income Including Noncontrolling Interest	21,395
Comprehensive Loss Attributable to Noncontrolling Interest	(10)
Comprehensive Income Attributable to Tennant Company	21,405	44,820	22,552
Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net (Loss) Earnings Including Noncontrolling Interest	14,024	15,622	14,512
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	1,215	270	(1,082)
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	1,215	270	(1,082)
Total Comprehensive Income Including Noncontrolling Interest	15,239
Comprehensive Loss Attributable to Noncontrolling Interest	0
Comprehensive Income Attributable to Tennant Company	15,239	15,892	13,430
Non-Guarantor Subsidiaries
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net (Loss) Earnings Including Noncontrolling Interest	19,977	8,842	(2,763)
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	2,960	3,534	(12,903)
Pension and retiree medical benefits	538	(1,691)	1,571
Cash flow hedge	0	0	0
Income Taxes:
Foreign currency translation adjustments	310	32	25
Pension and retiree medical benefits	(99)	296	(314)
Cash flow hedge	0	0	0
Total Other Comprehensive (Loss) Income, net of tax	3,709	2,171	(11,621)
Total Comprehensive Income Including Noncontrolling Interest	23,686
Comprehensive Loss Attributable to Noncontrolling Interest	(10)
Comprehensive Income Attributable to Tennant Company	23,696	11,013	(14,384)
Consolidation, Eliminations
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net (Loss) Earnings Including Noncontrolling Interest	(34,001)	(24,464)	(11,749)
Other Comprehensive Income (Loss):
Foreign currency translation adjustments	(4,175)	(3,804)	13,985
Pension and retiree medical benefits	(538)	1,691	(1,571)
Cash flow hedge	0	0	0
Income Taxes:
Foreign currency translation adjustments	(310)	(32)	(25)
Pension and retiree medical benefits	99	(296)	314
Cash flow hedge	0	0	0
Total Other Comprehensive (Loss) Income, net of tax	(4,924)	(2,441)	12,703
Total Comprehensive Income Including Noncontrolling Interest	(38,925)
Comprehensive Loss Attributable to Noncontrolling Interest	10
Comprehensive Income Attributable to Tennant Company	$ (38,935)	$ (26,905)	$ 954

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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