Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues	$ 299.7		$ 292.2		$ 562.1	$ 565.0
Cost of Sales	(178.9)		(175.0)		(333.1)	(338.7)
Gross Profit	120.8		117.2		229.0	226.3
Operating Expense:
Research and Development Expense	8.4		7.9		15.6	15.9
Selling and Administrative Expense	92.5		90.3		182.7	181.0
Total Operating Expense	100.9		98.2		198.3	196.9
Profit from Operations	19.9		19.0		30.7	29.4
Other Income (Expense):
Equity in Earnings of Affiliates	0.0		0.0		0.0	0.0
Interest (Expense) Income, Net	(4.5)		(5.1)		(8.8)	(10.1)
Intercompany Interest Income (Expense)	0.0		0.0		0.0	0.0
Net Foreign Currency Transaction Gain (Loss)	(0.2)		(0.3)		0.0	(1.1)
Other Expense, Net	1.4		(0.5)		1.3	(0.7)
Total Other Expense, Net	(3.3)		(5.9)		(7.5)	(11.9)
Profit Before Income Taxes	16.6		13.1		23.2	17.5
Income Tax Expense	1.8		0.4		3.0	1.4
Net Earnings Including Noncontrolling Interest	14.8	$ 5.4	12.7	$ 3.3	20.2	16.1
Net Earnings Attributable to Noncontrolling Interest	0.0		0.0		0.0	0.1
Net Earnings Attributable to Tennant Company	14.8		12.7		20.2	16.0
Eliminations
Revenues	(164.1)		(149.1)		(299.8)	(278.8)
Cost of Sales	162.7		149.1		296.6	277.5
Gross Profit	(1.4)		0.0		(3.2)	(1.3)
Operating Expense:
Research and Development Expense	0.0		0.0		0.0	0.0
Selling and Administrative Expense	0.0		0.0		0.0	0.0
Total Operating Expense	0.0		0.0		0.0	0.0
Profit from Operations	(1.4)		0.0		(3.2)	(1.3)
Other Income (Expense):
Equity in Earnings of Affiliates	(5.9)		(12.0)		(8.4)	(19.5)
Interest (Expense) Income, Net	0.0		0.0		0.0	0.0
Intercompany Interest Income (Expense)	0.0		0.0		0.0	0.0
Net Foreign Currency Transaction Gain (Loss)	0.0		0.0		0.0	0.0
Other Expense, Net	(0.1)		0.0		(0.1)	(0.1)
Total Other Expense, Net	(6.0)		(12.0)		(8.5)	(19.6)
Profit Before Income Taxes	(7.4)		(12.0)		(11.7)	(20.9)
Income Tax Expense	(0.7)		(1.4)		(2.8)	(3.9)
Net Earnings Including Noncontrolling Interest	(6.7)		(10.6)		(8.9)	(17.0)
Net Earnings Attributable to Noncontrolling Interest						(0.1)
Net Earnings Attributable to Tennant Company	(6.7)		(10.6)		(8.9)	(16.9)
Parent
Revenues	141.0		126.3		257.5	240.0
Cost of Sales	(92.5)		(85.1)		(168.9)	(162.3)
Gross Profit	48.5		41.2		88.6	77.7
Operating Expense:
Research and Development Expense	6.8		6.4		12.4	12.5
Selling and Administrative Expense	27.6		28.6		54.9	57.7
Total Operating Expense	34.4		35.0		67.3	70.2
Profit from Operations	14.1		6.2		21.3	7.5
Other Income (Expense):
Equity in Earnings of Affiliates	4.4		10.0		4.7	14.4
Interest (Expense) Income, Net	(4.5)		(5.4)		(8.8)	(10.5)
Intercompany Interest Income (Expense)	3.3		3.6		6.9	7.3
Net Foreign Currency Transaction Gain (Loss)	0.2		(0.6)		0.2	(0.3)
Other Expense, Net	(0.9)		(0.7)		(1.1)	(0.9)
Total Other Expense, Net	2.5		6.9		1.9	10.0
Profit Before Income Taxes	16.6		13.1		23.2	17.5
Income Tax Expense	1.8		0.4		3.0	1.4
Net Earnings Including Noncontrolling Interest	14.8		12.7		20.2	16.1
Net Earnings Attributable to Noncontrolling Interest						0.1
Net Earnings Attributable to Tennant Company	14.8		12.7		20.2	16.0
Guarantor Subsidiaries
Revenues	175.0		163.9		323.3	312.3
Cost of Sales	(148.1)		(137.2)		(271.0)	(260.3)
Gross Profit	26.9		26.7		52.3	52.0
Operating Expense:
Research and Development Expense	0.3		0.4		0.5	0.6
Selling and Administrative Expense	19.6		19.3		38.6	39.0
Total Operating Expense	19.9		19.7		39.1	39.6
Profit from Operations	7.0		7.0		13.2	12.4
Other Income (Expense):
Equity in Earnings of Affiliates	0.6		0.6		1.4	1.1
Interest (Expense) Income, Net	0.0		0.0		0.0	0.0
Intercompany Interest Income (Expense)	(1.4)		(1.4)		(2.8)	(2.8)
Net Foreign Currency Transaction Gain (Loss)	0.0		0.0		0.0	0.0
Other Expense, Net	(0.3)		(0.6)		(0.7)	(1.2)
Total Other Expense, Net	(1.1)		(1.4)		(2.1)	(2.9)
Profit Before Income Taxes	5.9		5.6		11.1	9.5
Income Tax Expense	1.9		1.4		3.0	2.3
Net Earnings Including Noncontrolling Interest	4.0		4.2		8.1	7.2
Net Earnings Attributable to Noncontrolling Interest						0.0
Net Earnings Attributable to Tennant Company	4.0		4.2		8.1	7.2
Non-Guarantor Subsidiaries
Revenues	147.8		151.1		281.1	291.5
Cost of Sales	(101.0)		(101.8)		(189.8)	(193.6)
Gross Profit	46.8		49.3		91.3	97.9
Operating Expense:
Research and Development Expense	1.3		1.1		2.7	2.8
Selling and Administrative Expense	45.3		42.4		89.2	84.3
Total Operating Expense	46.6		43.5		91.9	87.1
Profit from Operations	0.2		5.8		(0.6)	10.8
Other Income (Expense):
Equity in Earnings of Affiliates	0.9		1.4		2.3	4.0
Interest (Expense) Income, Net	0.0		0.3		0.0	0.4
Intercompany Interest Income (Expense)	(1.9)		(2.2)		(4.1)	(4.5)
Net Foreign Currency Transaction Gain (Loss)	(0.4)		0.3		(0.2)	(0.8)
Other Expense, Net	2.7		0.8		3.2	1.5
Total Other Expense, Net	1.3		0.6		1.2	0.6
Profit Before Income Taxes	1.5		6.4		0.6	11.4
Income Tax Expense	(1.2)		0.0		(0.2)	1.6
Net Earnings Including Noncontrolling Interest	2.7		6.4		0.8	9.8
Net Earnings Attributable to Noncontrolling Interest						0.1
Net Earnings Attributable to Tennant Company	$ 2.7		$ 6.4		$ 0.8	$ 9.7