Note 8 - Debt (Details Textual) $ in Millions		3 Months Ended
		Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2017
Finance Lease, Liability, Current		$ 0.1
Debt, Current, Total	[1]	$ 36.4	$ 10.9
Debt, Weighted Average Interest Rate, Net of Currency Swap Contract		4.40%
Secured Debt [Member]
Long-term Debt, Current Maturities, Total		$ 0.7
Debt Including Related Cross-currency Swap Instrument [Member]
Debt, Weighted Average Interest Rate		5.50%
Tennant Sales and Service Company [Member]
Noncontrolling Interest, Ownership Percentage by Parent		100.00%
The 2017 Credit Agreement [Member]
Debt Instrument, Covenant, Adjusted EBITDA, Maximum				4.00
Debt Instrument, Covenant, Adjusted EBITDA to Interest Expense Ratio, Minimum				3.50
Debt Instrument, Covenant, Senior Secured Net Indebtedness to Adjusted EBITDA Ratio, Maximum				3.50
Long-term Debt, Current Maturities, Total		$ 35.6
Long-term Debt, Total		10.0
Line of Credit Facility, Commitment Fee Amount		0.2
Debt Instrument, Unused Borrowing Capacity, Amount		186.8
The 2017 Credit Agreement [Member] | Letter of Credit [Member]
Long-term Line of Credit, Total		3.2
Senior Unsecured Notes [Member]
Long-term Debt, Total		$ 300.0

[1] The Company has the ability and intent to repay $35.6 million in outstanding credit facility borrowings, $0.7 million of current maturities of secured borrowings and $0.1 million of current maturities of finance lease liabilities over the next 12 months. Therefore, $36.4 million of debt has been classified as a current liability on the Consolidated Balance Sheet at March 31, 2021.