Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash, Cash Equivalents and Restricted Cash	$ 71.7			$ 86.1	$ 54.1			$ 59.0
Net Receivables	212.7			216.2
Intercompany Receivables	0.0			0.0
Inventories	160.9			135.1
Prepaid and Other Current Assets	34.2			31.2
Total Current Assets	479.5			468.6
Property, Plant and Equipment	411.6			386.6
Accumulated Depreciation	(244.1)			(223.2)
Property, Plant and Equipment, Net	167.5			163.4
Operating lease assets	46.2			0.0
Investment in Affiliates	0.0			0.0
Intercompany Loans	0.0			0.0
Goodwill	185.4			182.7
Intangible Assets, Net	139.5			146.5
Other Assets	27.0			31.3
Total Assets	1,045.1			992.5
Current Liabilities:
Current Portion of Long-Term Debt	20.2			27.0
Accounts Payable	93.9			98.4
Intercompany Payables	0.0			0.0
Employee Compensation and Benefits	52.9			56.1
Other Current Liabilities	102.9			67.4
Total Current Liabilities	269.9			248.9
Long-Term Liabilities:
Long-Term Debt	322.2			328.1
Intercompany Loans	0.0			0.0
Long-Term Operating Lease Liabilities	29.8			0.0
Employee-Related Benefits	19.5			21.1
Deferred Income Taxes	42.4			46.0
Other Liabilities	21.5			32.1
Total Long-Term Liabilities	435.4			427.3
Total Liabilities	705.3			676.2
Common Stock	6.8			6.8
Additional Paid-In Capital	39.7			28.5
Retained Earnings	339.1			316.3
Accumulated Other Comprehensive Loss	(47.3)			(37.2)
Total Tennant Company Shareholders' Equity	338.3			314.4
Noncontrolling Interest	1.5			1.9
Total Equity	339.8	$ 335.2	$ 320.2	316.3	309.1	$ 302.2	$ 307.4	298.5
Total Liabilities and Total Equity	1,045.1			992.5
Eliminations
Current Assets:
Cash, Cash Equivalents and Restricted Cash	0.0			0.0	0.0			0.0
Net Receivables	0.0			0.0
Intercompany Receivables	(148.3)			(178.9)
Inventories	(13.5)			(10.1)
Prepaid and Other Current Assets	0.7			(0.5)
Total Current Assets	(161.1)			(189.5)
Property, Plant and Equipment	0.0			0.0
Accumulated Depreciation	0.0			0.0
Property, Plant and Equipment, Net	0.0			0.0
Operating lease assets	0.0			0.0
Investment in Affiliates	(454.8)			(453.9)
Intercompany Loans	(293.5)			(304.8)
Goodwill	0.0			0.0
Intangible Assets, Net	0.0			0.0
Other Assets	0.0			0.0
Total Assets	(909.4)			(948.2)
Current Liabilities:
Current Portion of Long-Term Debt	0.0			0.0
Accounts Payable	0.0			0.0
Intercompany Payables	(148.3)			(179.0)
Employee Compensation and Benefits	0.0			0.0
Other Current Liabilities	0.7			(0.5)
Total Current Liabilities	(147.6)			(179.5)
Long-Term Liabilities:
Long-Term Debt	0.0			0.0
Intercompany Loans	(293.5)			(304.9)
Long-Term Operating Lease Liabilities	0.0			0.0
Employee-Related Benefits	0.0			0.0
Deferred Income Taxes	0.0			0.0
Other Liabilities	0.0			0.0
Total Long-Term Liabilities	(293.5)			(304.9)
Total Liabilities	(441.1)			(484.4)
Common Stock	(11.1)			(11.1)
Additional Paid-In Capital	(494.9)			(477.0)
Retained Earnings	(36.3)			(34.1)
Accumulated Other Comprehensive Loss	75.5			60.3
Total Tennant Company Shareholders' Equity	(466.8)			(461.9)
Noncontrolling Interest	(1.5)			(1.9)
Total Equity	(468.3)			(463.8)
Total Liabilities and Total Equity	(909.4)			(948.2)
Parent
Current Assets:
Cash, Cash Equivalents and Restricted Cash	30.2			24.8	18.1			18.5
Net Receivables	1.0			0.9
Intercompany Receivables	24.2			30.0
Inventories	44.1			37.1
Prepaid and Other Current Assets	19.8			17.5
Total Current Assets	119.3			110.3
Property, Plant and Equipment	250.3			229.8
Accumulated Depreciation	(170.7)			(159.4)
Property, Plant and Equipment, Net	79.6			70.4
Operating lease assets	5.4			0.0
Investment in Affiliates	402.9			421.0
Intercompany Loans	293.5			301.6
Goodwill	12.9			12.9
Intangible Assets, Net	3.4			4.0
Other Assets	5.7			11.0
Total Assets	922.7			931.2
Current Liabilities:
Current Portion of Long-Term Debt	19.0			21.8
Accounts Payable	42.8			41.0
Intercompany Payables	123.3			149.5
Employee Compensation and Benefits	15.4			14.4
Other Current Liabilities	30.4			22.8
Total Current Liabilities	230.9			249.5
Long-Term Liabilities:
Long-Term Debt	321.0			326.5
Intercompany Loans	3.8			3.3
Long-Term Operating Lease Liabilities	4.6			0.0
Employee-Related Benefits	10.7			11.0
Deferred Income Taxes	0.0			0.0
Other Liabilities	11.9			24.6
Total Long-Term Liabilities	352.0			365.4
Total Liabilities	582.9			614.9
Common Stock	6.8			6.8
Additional Paid-In Capital	39.7			28.5
Retained Earnings	339.1			316.3
Accumulated Other Comprehensive Loss	(47.3)			(37.2)
Total Tennant Company Shareholders' Equity	338.3			314.4
Noncontrolling Interest	1.5			1.9
Total Equity	339.8			316.3
Total Liabilities and Total Equity	922.7			931.2
Guarantor Subsidiaries
Current Assets:
Cash, Cash Equivalents and Restricted Cash	1.3			1.6	0.7			0.5
Net Receivables	104.7			94.8
Intercompany Receivables	124.1			148.9
Inventories	19.5			13.4
Prepaid and Other Current Assets	1.0			1.2
Total Current Assets	250.6			259.9
Property, Plant and Equipment	12.9			12.7
Accumulated Depreciation	(7.2)			(6.9)
Property, Plant and Equipment, Net	5.7			5.8
Operating lease assets	9.9			0.0
Investment in Affiliates	13.5			12.1
Intercompany Loans	0.0			0.0
Goodwill	1.7			1.7
Intangible Assets, Net	2.5			2.7
Other Assets	4.2			3.1
Total Assets	288.1			285.3
Current Liabilities:
Current Portion of Long-Term Debt	0.0			0.0
Accounts Payable	6.2			5.0
Intercompany Payables	0.0			0.0
Employee Compensation and Benefits	13.1			17.2
Other Current Liabilities	20.5			17.6
Total Current Liabilities	39.8			39.8
Long-Term Liabilities:
Long-Term Debt	0.0			0.0
Intercompany Loans	128.0			128.1
Long-Term Operating Lease Liabilities	4.8			0.0
Employee-Related Benefits	1.4			2.0
Deferred Income Taxes	0.0			0.0
Other Liabilities	2.9			2.9
Total Long-Term Liabilities	137.1			133.0
Total Liabilities	176.9			172.8
Common Stock	0.0			0.0
Additional Paid-In Capital	77.5			77.5
Retained Earnings	35.3			36.6
Accumulated Other Comprehensive Loss	(1.6)			(1.6)
Total Tennant Company Shareholders' Equity	111.2			112.5
Noncontrolling Interest	0.0			0.0
Total Equity	111.2			112.5
Total Liabilities and Total Equity	288.1			285.3
Non-Guarantor Subsidiaries
Current Assets:
Cash, Cash Equivalents and Restricted Cash	40.2			59.7	$ 35.3			$ 40.0
Net Receivables	107.0			120.5
Intercompany Receivables	0.0			0.0
Inventories	110.8			94.7
Prepaid and Other Current Assets	12.7			13.0
Total Current Assets	270.7			287.9
Property, Plant and Equipment	148.4			144.1
Accumulated Depreciation	(66.2)			(56.9)
Property, Plant and Equipment, Net	82.2			87.2
Operating lease assets	30.9			0.0
Investment in Affiliates	38.4			20.8
Intercompany Loans	0.0			3.2
Goodwill	170.8			168.1
Intangible Assets, Net	133.6			139.8
Other Assets	17.1			17.2
Total Assets	743.7			724.2
Current Liabilities:
Current Portion of Long-Term Debt	1.2			5.2
Accounts Payable	44.9			52.4
Intercompany Payables	25.0			29.5
Employee Compensation and Benefits	24.4			24.5
Other Current Liabilities	51.3			27.5
Total Current Liabilities	146.8			139.1
Long-Term Liabilities:
Long-Term Debt	1.2			1.6
Intercompany Loans	161.7			173.5
Long-Term Operating Lease Liabilities	20.4			0.0
Employee-Related Benefits	7.4			8.1
Deferred Income Taxes	42.4			46.0
Other Liabilities	6.7			4.6
Total Long-Term Liabilities	239.8			233.8
Total Liabilities	386.6			372.9
Common Stock	11.1			11.1
Additional Paid-In Capital	417.4			399.5
Retained Earnings	1.0			(2.5)
Accumulated Other Comprehensive Loss	(73.9)			(58.7)
Total Tennant Company Shareholders' Equity	355.6			349.4
Noncontrolling Interest	1.5			1.9
Total Equity	357.1			351.3
Total Liabilities and Total Equity	$ 743.7			$ 724.2