Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and Cash Equivalents	$ 54,001	$ 58,398
Restricted Cash	645	653
Net Receivables	212,265	209,516
Intercompany Receivables	0	0
Inventories	140,290	127,694
Prepaid Expenses	21,537	19,351
Other Current Assets	5,942	7,503
Total Current Assets	434,680	423,115
Property, Plant and Equipment	387,130	382,768
Accumulated Depreciation	(209,204)	(202,750)
Property, Plant and Equipment, Net	177,926	180,018
Deferred Income Taxes	14,832	11,134
Investment in Affiliates	0	0
Intercompany Loans	0	0
Goodwill	196,165	186,044
Intangible Assets, Net	172,297	172,347
Other Assets	20,002	21,319
Total Assets	1,015,902	993,977
Current Liabilities:
Current Portion of Long-Term Debt	30,902	30,883
Accounts Payable	102,702	96,082
Intercompany Payables	0	0
Employee Compensation and Benefits	34,674	37,257
Income Taxes Payable	2,800	2,838
Other Current Liabilities	70,293	69,447
Total Current Liabilities	241,371	236,507
Long-Term Liabilities:
Long-Term Debt	342,420	345,956
Intercompany Loans	0	0
Employee-Related Benefits	23,394	23,867
Deferred Income Taxes	53,412	53,225
Other Liabilities	47,934	35,948
Total Long-Term Liabilities	467,160	458,996
Total Liabilities	708,531	695,503
Common Stock	6,717	6,705
Additional Paid-In Capital	18,295	15,089
Retained Earnings	297,717	297,032
Accumulated Other Comprehensive Loss	(17,244)	(22,323)
Total Tennant Company Shareholders' Equity	305,485	296,503
Noncontrolling Interest	1,886	1,971
Total Equity	307,371	298,474
Total Liabilities and Total Equity	1,015,902	993,977
Eliminations
Current Assets:
Cash and Cash Equivalents	0	0
Restricted Cash	0	0
Net Receivables	0	0
Intercompany Receivables	(185,740)	(187,222)
Inventories	(10,234)	(8,993)
Prepaid Expenses	0	0
Other Current Assets	0	0
Total Current Assets	(195,974)	(196,215)
Property, Plant and Equipment	0	0
Accumulated Depreciation	0	0
Property, Plant and Equipment, Net	0	0
Deferred Income Taxes	0	0
Investment in Affiliates	(442,331)	(424,570)
Intercompany Loans	(318,595)	(309,805)
Goodwill	0	0
Intangible Assets, Net	0	0
Other Assets	0	0
Total Assets	(956,900)	(930,590)
Current Liabilities:
Current Portion of Long-Term Debt	0	0
Accounts Payable	0	0
Intercompany Payables	(185,740)	(187,222)
Employee Compensation and Benefits	0	0
Income Taxes Payable	0	0
Other Current Liabilities	0	0
Total Current Liabilities	(185,740)	(187,222)
Long-Term Liabilities:
Long-Term Debt	0	0
Intercompany Loans	(318,595)	(309,805)
Employee-Related Benefits	0	0
Deferred Income Taxes	0	0
Other Liabilities	0	0
Total Long-Term Liabilities	(318,595)	(309,805)
Total Liabilities	(504,335)	(497,027)
Common Stock	(11,131)	(11,131)
Additional Paid-In Capital	(462,011)	(456,943)
Retained Earnings	(8,905)	(2,578)
Accumulated Other Comprehensive Loss	31,368	39,060
Total Tennant Company Shareholders' Equity	(450,679)	(431,592)
Noncontrolling Interest	(1,886)	(1,971)
Total Equity	(452,565)	(433,563)
Total Liabilities and Total Equity	(956,900)	(930,590)
Parent
Current Assets:
Cash and Cash Equivalents	14,767	18,469
Restricted Cash	0	0
Net Receivables	605	683
Intercompany Receivables	54,461	53,444
Inventories	32,287	29,450
Prepaid Expenses	11,781	8,774
Other Current Assets	3,864	4,030
Total Current Assets	117,765	114,850
Property, Plant and Equipment	224,426	225,064
Accumulated Depreciation	(148,975)	(146,320)
Property, Plant and Equipment, Net	75,451	78,744
Deferred Income Taxes	2,178	1,308
Investment in Affiliates	408,509	392,486
Intercompany Loans	314,905	304,822
Goodwill	12,869	12,869
Intangible Assets, Net	2,974	2,105
Other Assets	9,083	10,363
Total Assets	943,734	917,547
Current Liabilities:
Current Portion of Long-Term Debt	29,460	29,413
Accounts Payable	42,583	39,927
Intercompany Payables	131,279	133,778
Employee Compensation and Benefits	8,976	8,311
Income Taxes Payable	341	366
Other Current Liabilities	27,447	20,183
Total Current Liabilities	240,086	231,978
Long-Term Liabilities:
Long-Term Debt	340,447	344,147
Intercompany Loans	3,690	0
Employee-Related Benefits	12,576	11,160
Deferred Income Taxes	0	0
Other Liabilities	39,564	31,788
Total Long-Term Liabilities	396,277	387,095
Total Liabilities	636,363	619,073
Common Stock	6,717	6,705
Additional Paid-In Capital	18,295	15,089
Retained Earnings	297,717	297,032
Accumulated Other Comprehensive Loss	(17,244)	(22,323)
Total Tennant Company Shareholders' Equity	305,485	296,503
Noncontrolling Interest	1,886	1,971
Total Equity	307,371	298,474
Total Liabilities and Total Equity	943,734	917,547
Guarantor Subsidiaries
Current Assets:
Cash and Cash Equivalents	2,078	507
Restricted Cash	0	0
Net Receivables	85,079	88,629
Intercompany Receivables	131,279	133,778
Inventories	16,076	12,695
Prepaid Expenses	275	1,172
Other Current Assets	404	0
Total Current Assets	235,191	236,781
Property, Plant and Equipment	12,738	12,155
Accumulated Depreciation	(6,502)	(6,333)
Property, Plant and Equipment, Net	6,236	5,822
Deferred Income Taxes	3,233	2,669
Investment in Affiliates	11,562	11,273
Intercompany Loans	0	0
Goodwill	1,739	1,739
Intangible Assets, Net	2,862	2,898
Other Assets	(427)	0
Total Assets	260,396	261,182
Current Liabilities:
Current Portion of Long-Term Debt	0	0
Accounts Payable	4,029	3,018
Intercompany Payables	1,360	1,963
Employee Compensation and Benefits	8,194	10,355
Income Taxes Payable	0	0
Other Current Liabilities	10,780	15,760
Total Current Liabilities	24,363	31,096
Long-Term Liabilities:
Long-Term Debt	0	0
Intercompany Loans	128,000	128,000
Employee-Related Benefits	1,869	3,992
Deferred Income Taxes	0	0
Other Liabilities	2,669	2,483
Total Long-Term Liabilities	132,538	134,475
Total Liabilities	156,901	165,571
Common Stock	0	0
Additional Paid-In Capital	77,551	72,483
Retained Earnings	26,777	23,797
Accumulated Other Comprehensive Loss	(833)	(669)
Total Tennant Company Shareholders' Equity	103,495	95,611
Noncontrolling Interest	0	0
Total Equity	103,495	95,611
Total Liabilities and Total Equity	260,396	261,182
Non-Guarantor Subsidiaries
Current Assets:
Cash and Cash Equivalents	37,156	39,422
Restricted Cash	645	653
Net Receivables	126,581	120,204
Intercompany Receivables	0	0
Inventories	102,161	94,542
Prepaid Expenses	9,481	9,405
Other Current Assets	1,674	3,473
Total Current Assets	277,698	267,699
Property, Plant and Equipment	149,966	145,549
Accumulated Depreciation	(53,727)	(50,097)
Property, Plant and Equipment, Net	96,239	95,452
Deferred Income Taxes	9,421	7,157
Investment in Affiliates	22,260	20,811
Intercompany Loans	3,690	4,983
Goodwill	181,557	171,436
Intangible Assets, Net	166,461	167,344
Other Assets	11,346	10,956
Total Assets	768,672	745,838
Current Liabilities:
Current Portion of Long-Term Debt	1,442	1,470
Accounts Payable	56,090	53,137
Intercompany Payables	53,101	51,481
Employee Compensation and Benefits	17,504	18,591
Income Taxes Payable	2,459	2,472
Other Current Liabilities	32,066	33,504
Total Current Liabilities	162,662	160,655
Long-Term Liabilities:
Long-Term Debt	1,973	1,809
Intercompany Loans	186,905	181,805
Employee-Related Benefits	8,949	8,715
Deferred Income Taxes	53,412	53,225
Other Liabilities	5,701	1,677
Total Long-Term Liabilities	256,940	247,231
Total Liabilities	419,602	407,886
Common Stock	11,131	11,131
Additional Paid-In Capital	384,460	384,460
Retained Earnings	(17,872)	(21,219)
Accumulated Other Comprehensive Loss	(30,535)	(38,391)
Total Tennant Company Shareholders' Equity	347,184	335,981
Noncontrolling Interest	1,886	1,971
Total Equity	349,070	337,952
Total Liabilities and Total Equity	$ 768,672	$ 745,838