Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues	$ 280.7			$ 273.3			$ 842.8	$ 838.3
Cost of Sales	(166.7)			(166.7)			(499.8)	(505.4)
Gross Profit	114.0			106.6			343.0	332.9
Operating Expense:
Research and Development Expense	8.2			7.5			23.8	23.4
Selling and Administrative Expense	84.3			83.7			267.0	264.7
Total Operating Expense	92.5			91.2			290.8	288.1
Profit from Operations	21.5			15.4			52.2	44.8
Other Income (Expense):
Equity in Earnings of Affiliates	0.0			0.0			0.0	0.0
Interest (Expense) Income, Net	(4.4)			(5.2)			(13.2)	(15.2)
Intercompany Interest Income (Expense)	0.0			0.0			0.0	0.0
Net Foreign Currency Transaction Losses	(0.6)			(0.3)			(0.6)	(1.4)
Other Income (Expense), Net	0.1			0.0			1.4	(0.8)
Total Other Expense, Net	(4.9)			(5.5)			(12.4)	(17.4)
Profit Before Income Taxes	16.6			9.9			39.8	27.4
Income Tax Expense	2.0			0.2			5.0	1.6
Net Earnings Including Noncontrolling Interest	14.6	$ 14.8	$ 5.4	9.7	$ 12.7	$ 3.3	34.8	25.8
Net Earnings Attributable to Noncontrolling Interest	0.0			0.0			0.0	0.1
Net Earnings Attributable to Tennant Company	14.6			9.7			34.8	25.7
Eliminations
Revenues	(155.2)			(144.4)			(455.0)	(423.2)
Cost of Sales	155.1			144.3			451.7	421.8
Gross Profit	(0.1)			(0.1)			(3.3)	(1.4)
Operating Expense:
Research and Development Expense	0.0			0.0			0.0	0.0
Selling and Administrative Expense	0.0			0.8			0.0	0.8
Total Operating Expense	0.0			0.8			0.0	0.8
Profit from Operations	(0.1)			(0.9)			(3.3)	(2.2)
Other Income (Expense):
Equity in Earnings of Affiliates	(7.9)			(5.7)			(16.3)	(25.2)
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 Losses	0.0			0.0			0.0	0.0
Other Income (Expense), Net	0.0			0.8			(0.1)	0.7
Total Other Expense, Net	(7.9)			(4.9)			(16.4)	(24.5)
Profit Before Income Taxes	(8.0)			(5.8)			(19.7)	(26.7)
Income Tax Expense	(0.7)			(0.3)			(3.5)	(4.2)
Net Earnings Including Noncontrolling Interest	(7.3)			(5.5)			(16.2)	(22.5)
Net Earnings Attributable to Noncontrolling Interest								(0.1)
Net Earnings Attributable to Tennant Company	(7.3)			(5.5)			(16.2)	(22.4)
Parent
Revenues	136.0			126.1			393.5	366.1
Cost of Sales	(88.0)			(86.8)			(256.9)	(249.1)
Gross Profit	48.0			39.3			136.6	117.0
Operating Expense:
Research and Development Expense	6.6			6.1			19.0	18.6
Selling and Administrative Expense	30.8			26.7			85.7	84.5
Total Operating Expense	37.4			32.8			104.7	103.1
Profit from Operations	10.6			6.5			31.9	13.9
Other Income (Expense):
Equity in Earnings of Affiliates	7.2			5.3			11.9	19.7
Interest (Expense) Income, Net	(4.4)			(5.3)			(13.2)	(15.7)
Intercompany Interest Income (Expense)	3.6			3.6			10.5	10.9
Net Foreign Currency Transaction Losses	(0.2)			(0.1)			0.0	(0.4)
Other Income (Expense), Net	(0.2)			(0.1)			(1.3)	(1.0)
Total Other Expense, Net	6.0			3.4			7.9	13.5
Profit Before Income Taxes	16.6			9.9			39.8	27.4
Income Tax Expense	2.0			0.2			5.0	1.6
Net Earnings Including Noncontrolling Interest	14.6			9.7			34.8	25.8
Net Earnings Attributable to Noncontrolling Interest								0.1
Net Earnings Attributable to Tennant Company	14.6			9.7			34.8	25.7
Guarantor Subsidiaries
Revenues	172.6			160.2			495.9	472.5
Cost of Sales	(147.2)			(135.0)			(418.2)	(395.3)
Gross Profit	25.4			25.2			77.7	77.2
Operating Expense:
Research and Development Expense	0.2			0.3			0.7	0.8
Selling and Administrative Expense	18.3			18.1			56.9	57.2
Total Operating Expense	18.5			18.4			57.6	58.0
Profit from Operations	6.9			6.8			20.1	19.2
Other Income (Expense):
Equity in Earnings of Affiliates	0.2			0.2			1.6	1.3
Interest (Expense) Income, Net	0.0			0.0			0.0	0.0
Intercompany Interest Income (Expense)	(1.5)			(1.4)			(4.3)	(4.3)
Net Foreign Currency Transaction Losses	0.0			0.0			0.0	0.0
Other Income (Expense), Net	(0.3)			(0.5)			(1.0)	(1.6)
Total Other Expense, Net	(1.6)			(1.7)			(3.7)	(4.6)
Profit Before Income Taxes	5.3			5.1			16.4	14.6
Income Tax Expense	0.8			1.2			3.8	3.5
Net Earnings Including Noncontrolling Interest	4.5			3.9			12.6	11.1
Net Earnings Attributable to Noncontrolling Interest								0.0
Net Earnings Attributable to Tennant Company	4.5			3.9			12.6	11.1
Non-Guarantor Subsidiaries
Revenues	127.3			131.4			408.4	422.9
Cost of Sales	(86.6)			(89.2)			(276.4)	(282.8)
Gross Profit	40.7			42.2			132.0	140.1
Operating Expense:
Research and Development Expense	1.4			1.1			4.1	4.0
Selling and Administrative Expense	35.2			38.1			124.4	122.2
Total Operating Expense	36.6			39.2			128.5	126.2
Profit from Operations	4.1			3.0			3.5	13.9
Other Income (Expense):
Equity in Earnings of Affiliates	0.5			0.2			2.8	4.2
Interest (Expense) Income, Net	0.0			0.1			0.0	0.5
Intercompany Interest Income (Expense)	(2.1)			(2.2)			(6.2)	(6.6)
Net Foreign Currency Transaction Losses	(0.4)			(0.2)			(0.6)	(1.0)
Other Income (Expense), Net	0.6			(0.2)			3.8	1.1
Total Other Expense, Net	(1.4)			(2.3)			(0.2)	(1.8)
Profit Before Income Taxes	2.7			0.7			3.3	12.1
Income Tax Expense	(0.1)			(0.9)			(0.3)	0.7
Net Earnings Including Noncontrolling Interest	2.8			1.6			3.6	11.4
Net Earnings Attributable to Noncontrolling Interest								0.1
Net Earnings Attributable to Tennant Company	$ 2.8			$ 1.6			$ 3.6	$ 11.3