Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Sales	$ 292,197		$ 270,791	$ 565,044	$ 461,850
Cost of Sales	173,398		166,237	335,608	277,560
Gross Profit	118,799		104,554	229,436	184,290
Operating Expense:
Research and Development Expense	7,906		7,886	15,902	16,332
Selling and Administrative Expense	91,864		87,326	184,133	161,282
Total Operating Expense	99,770		95,212	200,035	177,614
Profit from Operations	19,029		9,342	29,401	6,676
Other Income (Expense):
Equity in Earnings of Affiliates	0		0	0	0
Interest (Expense) Income, Net	(5,053)		(11,040)	(10,049)	(11,750)
Intercompany Interest Income (Expense)	0		0	0	0
Net Foreign Currency Transaction Losses	(337)		(336)	(1,086)	(1,533)
Other Expense, Net	(510)		(384)	(760)	(352)
Total Other Expense, Net	(5,900)		(11,760)	(11,895)	(13,635)
Profit (Loss) Before Income Taxes	13,129		(2,418)	17,506	(6,959)
Income Tax Expense (Benefit)	363		238	1,440	(346)
Net Earnings (Loss) Including Noncontrolling Interest	12,766	$ 12,766	(2,656)	16,066	(6,613)
Net Earnings (Loss) Attributable to Noncontrolling Interest	22		(65)	48	(65)
Net Earnings (Loss) Attributable to Tennant Company	12,744		(2,591)	16,018	(6,548)
Eliminations
Net Sales	(149,035)		(137,078)	(278,706)	(259,638)
Cost of Sales	(149,054)		(137,568)	(277,445)	(259,156)
Gross Profit	19		490	(1,261)	(482)
Operating Expense:
Research and Development Expense	0		0	0	0
Selling and Administrative Expense	0		0	0	0
Total Operating Expense	0		0	0	0
Profit from Operations	19		490	(1,261)	(482)
Other Income (Expense):
Equity in Earnings of Affiliates	(11,996)		(3,941)	(19,524)	(5,920)
Interest (Expense) Income, Net	(10)		(12)	(19)	(12)
Intercompany Interest Income (Expense)	0		0	0	0
Net Foreign Currency Transaction Losses	0		0	0	0
Other Expense, Net	(36)		(35)	(60)	(35)
Total Other Expense, Net	(12,042)		(3,988)	(19,603)	(5,967)
Profit (Loss) Before Income Taxes	(12,023)		(3,498)	(20,864)	(6,449)
Income Tax Expense (Benefit)	(1,372)		(5,520)	(3,860)	(6,067)
Net Earnings (Loss) Including Noncontrolling Interest	(10,651)	(10,651)	2,022	(17,004)	(382)
Net Earnings (Loss) Attributable to Noncontrolling Interest	(22)		65	(48)	65
Net Earnings (Loss) Attributable to Tennant Company	(10,629)		1,957	(16,956)	(447)
Parent
Net Sales	126,293		120,153	239,983	225,858
Cost of Sales	85,053		82,182	162,284	153,779
Gross Profit	41,240		37,971	77,699	72,079
Operating Expense:
Research and Development Expense	6,422		6,579	12,529	14,525
Selling and Administrative Expense	28,625		30,135	57,713	62,199
Total Operating Expense	35,047		36,714	70,242	76,724
Profit from Operations	6,193		1,257	7,457	(4,645)
Other Income (Expense):
Equity in Earnings of Affiliates	10,026		3,145	14,401	4,795
Interest (Expense) Income, Net	(5,388)		(10,827)	(10,496)	(11,591)
Intercompany Interest Income (Expense)	3,643		3,499	7,368	4,968
Net Foreign Currency Transaction Losses	(639)		1,033	(285)	196
Other Expense, Net	(706)		(525)	(939)	(682)
Total Other Expense, Net	6,936		(3,675)	10,049	(2,314)
Profit (Loss) Before Income Taxes	13,129		(2,418)	17,506	(6,959)
Income Tax Expense (Benefit)	363		238	1,440	(346)
Net Earnings (Loss) Including Noncontrolling Interest	12,766	12,766	(2,656)	16,066	(6,613)
Net Earnings (Loss) Attributable to Noncontrolling Interest	22		(65)	48	(65)
Net Earnings (Loss) Attributable to Tennant Company	12,744		(2,591)	16,018	(6,548)
Guarantor Subsidiaries
Net Sales	163,865		156,515	312,298	295,595
Cost of Sales	137,144		129,779	260,269	242,511
Gross Profit	26,721		26,736	52,029	53,084
Operating Expense:
Research and Development Expense	342		73	546	160
Selling and Administrative Expense	19,343		19,734	39,060	39,806
Total Operating Expense	19,685		19,807	39,606	39,966
Profit from Operations	7,036		6,929	12,423	13,118
Other Income (Expense):
Equity in Earnings of Affiliates	588		796	1,094	1,125
Interest (Expense) Income, Net	0		0	0	0
Intercompany Interest Income (Expense)	(1,436)		(1,441)	(2,858)	(2,869)
Net Foreign Currency Transaction Losses	(5)		(4)	(6)	(2)
Other Expense, Net	(546)		(150)	(1,137)	(225)
Total Other Expense, Net	(1,399)		(799)	(2,907)	(1,971)
Profit (Loss) Before Income Taxes	5,637		6,130	9,516	11,147
Income Tax Expense (Benefit)	1,391		1,898	2,290	3,469
Net Earnings (Loss) Including Noncontrolling Interest	4,246	4,246	4,232	7,226	7,678
Net Earnings (Loss) Attributable to Noncontrolling Interest	0		0	0	0
Net Earnings (Loss) Attributable to Tennant Company	4,246		4,232	7,226	7,678
Non-Guarantor Subsidiaries
Net Sales	151,074		131,201	291,469	200,035
Cost of Sales	100,255		91,844	190,500	140,426
Gross Profit	50,819		39,357	100,969	59,609
Operating Expense:
Research and Development Expense	1,142		1,234	2,827	1,647
Selling and Administrative Expense	43,896		37,457	87,360	59,277
Total Operating Expense	45,038		38,691	90,187	60,924
Profit from Operations	5,781		666	10,782	(1,315)
Other Income (Expense):
Equity in Earnings of Affiliates	1,382		0	4,029	0
Interest (Expense) Income, Net	345		(201)	466	(147)
Intercompany Interest Income (Expense)	(2,207)		(2,058)	(4,510)	(2,099)
Net Foreign Currency Transaction Losses	307		(1,365)	(795)	(1,727)
Other Expense, Net	778		326	1,376	590
Total Other Expense, Net	605		(3,298)	566	(3,383)
Profit (Loss) Before Income Taxes	6,386		(2,632)	11,348	(4,698)
Income Tax Expense (Benefit)	(19)		3,622	1,570	2,598
Net Earnings (Loss) Including Noncontrolling Interest	6,405	$ 6,405	(6,254)	9,778	(7,296)
Net Earnings (Loss) Attributable to Noncontrolling Interest	22		(65)	48	(65)
Net Earnings (Loss) Attributable to Tennant Company	$ 6,383		$ (6,189)	$ 9,730	$ (7,231)