Separate Financial Information of Guarantor Subsidiaries Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Net Sales	$ 285,212	$ 273,255	$ 292,197	$ 272,847	$ 279,295	$ 261,921	$ 270,791	$ 191,059	$ 1,123,511	$ 1,003,066	$ 808,572
Cost of Sales									678,478	603,253	456,977
Gross Profit	112,172	106,509	117,225	109,116	113,866	103,081	103,130	79,736	445,033	399,813	351,595
Operating Expense:
Research and Development Expense									30,739	32,013	34,738
Selling and Administrative Expense									356,316	334,782	248,592
Total Operating Expense									387,055	366,795	283,330
Profit from Operations									57,978	33,018	68,265
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									0	0	0
Interest (Expense) Income, Net									(20,307)	(22,989)	(949)
Intercompany Interest Income (Expense)									0	0	0
Net Foreign Currency Transaction Losses									(1,100)	(3,387)	(392)
Other (Expense) Income, Net									(729)	(7,934)	(433)
Total Other Expense, Net									(22,136)	(34,310)	(1,774)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									35,842	(1,292)	66,491
Income Tax Expense (Benefit)									2,304	4,913	19,877
Net Earnings (Loss) Including Noncontrolling Interest									33,538	(6,205)	46,614
Net Earnings Attributable to Noncontrolling Interest									126	(10)	0
Net Earnings (Loss) Attributable to Tennant Company	$ 7,717	$ 9,676	$ 12,744	$ 3,274	$ (3,206)	$ 3,559	$ (2,591)	$ (3,957)	33,412	(6,195)	46,614
Parent Company
Debt Instrument [Line Items]
Net Sales									494,341	454,703	455,375
Cost of Sales									336,398	311,897	299,459
Gross Profit									157,943	142,806	155,916
Operating Expense:
Research and Development Expense									24,455	27,219	32,378
Selling and Administrative Expense									116,528	110,414	95,340
Total Operating Expense									140,983	137,633	127,718
Profit from Operations									16,960	5,173	28,198
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									27,409	12,754	34,068
Interest (Expense) Income, Net									(20,466)	(22,659)	(1,204)
Intercompany Interest Income (Expense)									14,597	12,519	7,157
Net Foreign Currency Transaction Losses									(370)	857	648
Other (Expense) Income, Net									(2,288)	(9,936)	(2,376)
Total Other Expense, Net									18,882	(6,465)	38,293
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									35,842	(1,292)	66,491
Income Tax Expense (Benefit)									2,304	4,913	19,877
Net Earnings (Loss) Including Noncontrolling Interest									33,538	(6,205)	46,614
Net Earnings Attributable to Noncontrolling Interest									126	(10)
Net Earnings (Loss) Attributable to Tennant Company									33,412	(6,195)	46,614
Guarantor Subsidiaries
Debt Instrument [Line Items]
Net Sales									634,341	594,405	587,815
Cost of Sales									533,800	488,972	483,075
Gross Profit									100,541	105,433	104,740
Operating Expense:
Research and Development Expense									1,090	315	429
Selling and Administrative Expense									76,623	78,516	74,643
Total Operating Expense									77,713	78,831	75,072
Profit from Operations									22,828	26,602	29,668
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									2,249	2,004	2,192
Interest (Expense) Income, Net									0	0	0
Intercompany Interest Income (Expense)									(5,760)	(5,776)	(5,570)
Net Foreign Currency Transaction Losses									(21)	0	(652)
Other (Expense) Income, Net									(2,434)	(736)	(573)
Total Other Expense, Net									(5,966)	(4,508)	(4,603)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									16,862	22,094	25,065
Income Tax Expense (Benefit)									4,022	8,070	9,443
Net Earnings (Loss) Including Noncontrolling Interest									12,840	14,024	15,622
Net Earnings Attributable to Noncontrolling Interest									0	0
Net Earnings (Loss) Attributable to Tennant Company									12,840	14,024	15,622
Non-Guarantor Subsidiaries
Debt Instrument [Line Items]
Net Sales									570,627	471,559	290,349
Cost of Sales									383,010	321,759	199,336
Gross Profit									187,617	149,800	91,013
Operating Expense:
Research and Development Expense									5,194	4,479	1,931
Selling and Administrative Expense									161,911	145,852	78,609
Total Operating Expense									167,105	150,331	80,540
Profit from Operations									20,512	(531)	10,473
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									5,374	28,855	0
Interest (Expense) Income, Net									196	(299)	255
Intercompany Interest Income (Expense)									(8,837)	(6,743)	(1,587)
Net Foreign Currency Transaction Losses									(709)	(4,244)	(388)
Other (Expense) Income, Net									2,862	2,841	2,516
Total Other Expense, Net									(1,114)	20,410	796
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									19,398	19,879	11,269
Income Tax Expense (Benefit)									388	(98)	2,427
Net Earnings (Loss) Including Noncontrolling Interest									19,010	19,977	8,842
Net Earnings Attributable to Noncontrolling Interest									126	(10)
Net Earnings (Loss) Attributable to Tennant Company									18,884	19,987	8,842
Eliminations
Debt Instrument [Line Items]
Net Sales									(575,798)	(517,601)	(524,967)
Cost of Sales									(574,730)	(519,375)	(524,893)
Gross Profit									(1,068)	1,774	(74)
Operating Expense:
Research and Development Expense									0	0	0
Selling and Administrative Expense									1,254	0	0
Total Operating Expense									1,254	0	0
Profit from Operations									(2,322)	1,774	(74)
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									(35,032)	(43,613)	(36,260)
Interest (Expense) Income, Net									(37)	(31)	0
Intercompany Interest Income (Expense)									0	0	0
Net Foreign Currency Transaction Losses									0	0	0
Other (Expense) Income, Net									1,131	(103)	0
Total Other Expense, Net									(33,938)	(43,747)	(36,260)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									(36,260)	(41,973)	(36,334)
Income Tax Expense (Benefit)									(4,410)	(7,972)	(11,870)
Net Earnings (Loss) Including Noncontrolling Interest									(31,850)	(34,001)	(24,464)
Net Earnings Attributable to Noncontrolling Interest									(126)	10
Net Earnings (Loss) Attributable to Tennant Company									$ (31,724)	$ (34,011)	$ (24,464)