Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash, Cash Equivalents and Restricted Cash	$ 46.9	$ 86.1	$ 54.6	$ 59.0
Net Receivables	213.7	216.2
Intercompany Receivables	0.0	0.0
Inventories	158.2	135.1
Prepaid and Other Current Assets	33.6	31.2
Total Current Assets	452.4	468.6
Property, Plant and Equipment	405.7	386.6
Accumulated Depreciation	(230.8)	(223.2)
Property, Plant and Equipment, Net	174.9	163.4
Operating lease assets	40.7	0.0
Investment in Affiliates	0.0	0.0
Intercompany Loans	0.0	0.0
Goodwill	189.7	182.7
Intangible Assets, Net	156.0	146.5
Other Assets	27.0	31.3
Total Assets	1,040.7	992.5
Current Liabilities:
Current Portion of Long-Term Debt	30.1	27.0
Accounts Payable	94.9	98.4
Intercompany Payables	0.0	0.0
Employee Compensation and Benefits	41.6	56.1
Other Current Liabilities	100.6	67.4
Total Current Liabilities	267.2	248.9
Long-Term Liabilities:
Long-Term Debt	330.1	328.1
Intercompany Loans	0.0	0.0
Long-Term Operating Lease Liabilities	24.7	0.0
Employee-Related Benefits	20.6	21.1
Deferred Income Taxes	46.2	46.0
Other Liabilities	31.7	32.1
Total Long-Term Liabilities	453.3	427.3
Total Liabilities	720.5	676.2
Common Stock	6.8	6.8
Additional Paid-In Capital	32.0	28.5
Retained Earnings	317.7	316.3
Accumulated Other Comprehensive Loss	(38.5)	(37.2)
Total Tennant Company Shareholders' Equity	318.0	314.4
Noncontrolling Interest	2.2	1.9
Total Equity	320.2	316.3	307.4	298.5
Total Liabilities and Total Equity	1,040.7	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	(155.7)	(178.9)
Inventories	(11.8)	(10.1)
Prepaid and Other Current Assets	0.6	(0.5)
Total Current Assets	(166.9)	(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	(455.1)	(453.9)
Intercompany Loans	(298.4)	(304.8)
Goodwill	0.0	0.0
Intangible Assets, Net	0.0	0.0
Other Assets	0.0	0.0
Total Assets	(920.4)	(948.2)
Current Liabilities:
Current Portion of Long-Term Debt	0.0	0.0
Accounts Payable	0.0	0.0
Intercompany Payables	(155.7)	(179.0)
Employee Compensation and Benefits	0.0	0.0
Other Current Liabilities	0.6	(0.5)
Total Current Liabilities	(155.1)	(179.5)
Long-Term Liabilities:
Long-Term Debt	0.0	0.0
Intercompany Loans	(298.4)	(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	(298.4)	(304.9)
Total Liabilities	(453.5)	(484.4)
Common Stock	(11.1)	(11.1)
Additional Paid-In Capital	(494.5)	(477.0)
Retained Earnings	(22.0)	(34.1)
Accumulated Other Comprehensive Loss	62.9	60.3
Total Tennant Company Shareholders' Equity	(464.7)	(461.9)
Noncontrolling Interest	(2.2)	(1.9)
Total Equity	(466.9)	(463.8)
Total Liabilities and Total Equity	(920.4)	(948.2)
Parent
Current Assets:
Cash, Cash Equivalents and Restricted Cash	9.8	24.8	14.7	18.4
Net Receivables	1.0	0.9
Intercompany Receivables	30.6	30.0
Inventories	41.6	37.1
Prepaid and Other Current Assets	20.0	17.5
Total Current Assets	103.0	110.3
Property, Plant and Equipment	246.2	229.8
Accumulated Depreciation	(163.4)	(159.4)
Property, Plant and Equipment, Net	82.8	70.4
Operating lease assets	1.0	0.0
Investment in Affiliates	403.4	421.0
Intercompany Loans	298.4	301.6
Goodwill	12.9	12.9
Intangible Assets, Net	3.8	4.0
Other Assets	6.1	11.0
Total Assets	911.4	931.2
Current Liabilities:
Current Portion of Long-Term Debt	28.9	21.8
Accounts Payable	36.2	41.0
Intercompany Payables	125.7	149.5
Employee Compensation and Benefits	9.9	14.4
Other Current Liabilities	26.7	22.8
Total Current Liabilities	227.4	249.5
Long-Term Liabilities:
Long-Term Debt	328.6	326.5
Intercompany Loans	3.4	3.3
Long-Term Operating Lease Liabilities	0.5	0.0
Employee-Related Benefits	11.3	11.0
Deferred Income Taxes	0.0	0.0
Other Liabilities	20.0	24.6
Total Long-Term Liabilities	363.8	365.4
Total Liabilities	591.2	614.9
Common Stock	6.8	6.8
Additional Paid-In Capital	32.0	28.5
Retained Earnings	317.7	316.3
Accumulated Other Comprehensive Loss	(38.5)	(37.2)
Total Tennant Company Shareholders' Equity	318.0	314.4
Noncontrolling Interest	2.2	1.9
Total Equity	320.2	316.3
Total Liabilities and Total Equity	911.4	931.2
Guarantor Subsidiaries
Current Assets:
Cash, Cash Equivalents and Restricted Cash	1.1	1.6	2.1	0.5
Net Receivables	89.7	94.8
Intercompany Receivables	125.1	148.9
Inventories	17.9	13.4
Prepaid and Other Current Assets	0.9	1.2
Total Current Assets	234.7	259.9
Property, Plant and Equipment	13.1	12.7
Accumulated Depreciation	(6.6)	(6.9)
Property, Plant and Equipment, Net	6.5	5.8
Operating lease assets	9.9	0.0
Investment in Affiliates	12.8	12.1
Intercompany Loans	0.0	0.0
Goodwill	1.7	1.7
Intangible Assets, Net	2.6	2.7
Other Assets	3.3	3.1
Total Assets	271.5	285.3
Current Liabilities:
Current Portion of Long-Term Debt	0.0	0.0
Accounts Payable	5.1	5.0
Intercompany Payables	0.0	0.0
Employee Compensation and Benefits	8.1	17.2
Other Current Liabilities	18.4	17.6
Total Current Liabilities	31.6	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	1.5	2.0
Deferred Income Taxes	0.0	0.0
Other Liabilities	3.1	2.9
Total Long-Term Liabilities	137.4	133.0
Total Liabilities	169.0	172.8
Common Stock	0.0	0.0
Additional Paid-In Capital	77.6	77.5
Retained Earnings	26.5	36.6
Accumulated Other Comprehensive Loss	(1.6)	(1.6)
Total Tennant Company Shareholders' Equity	102.5	112.5
Noncontrolling Interest	0.0	0.0
Total Equity	102.5	112.5
Total Liabilities and Total Equity	271.5	285.3
Non-Guarantor Subsidiaries
Current Assets:
Cash, Cash Equivalents and Restricted Cash	36.0	59.7	$ 37.8	$ 40.1
Net Receivables	123.0	120.5
Intercompany Receivables	0.0	0.0
Inventories	110.5	94.7
Prepaid and Other Current Assets	12.1	13.0
Total Current Assets	281.6	287.9
Property, Plant and Equipment	146.4	144.1
Accumulated Depreciation	(60.8)	(56.9)
Property, Plant and Equipment, Net	85.6	87.2
Operating lease assets	29.8	0.0
Investment in Affiliates	38.9	20.8
Intercompany Loans	0.0	3.2
Goodwill	175.1	168.1
Intangible Assets, Net	149.6	139.8
Other Assets	17.6	17.2
Total Assets	778.2	724.2
Current Liabilities:
Current Portion of Long-Term Debt	1.2	5.2
Accounts Payable	53.6	52.4
Intercompany Payables	30.0	29.5
Employee Compensation and Benefits	23.6	24.5
Other Current Liabilities	54.9	27.5
Total Current Liabilities	163.3	139.1
Long-Term Liabilities:
Long-Term Debt	1.5	1.6
Intercompany Loans	167.0	173.5
Long-Term Operating Lease Liabilities	19.4	0.0
Employee-Related Benefits	7.8	8.1
Deferred Income Taxes	46.2	46.0
Other Liabilities	8.6	4.6
Total Long-Term Liabilities	250.5	233.8
Total Liabilities	413.8	372.9
Common Stock	11.1	11.1
Additional Paid-In Capital	416.9	399.5
Retained Earnings	(4.5)	(2.5)
Accumulated Other Comprehensive Loss	(61.3)	(58.7)
Total Tennant Company Shareholders' Equity	362.2	349.4
Noncontrolling Interest	2.2	1.9
Total Equity	364.4	351.3
Total Liabilities and Total Equity	$ 778.2	$ 724.2