Consolidated Statements of Operations - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Net Sales	$ 1,137,600,000	$ 1,123,500,000	$ 1,003,100,000
Cost of Sales	675,900,000	678,500,000	603,300,000
Gross Profit	461,700,000	445,000,000.0	399,800,000
Operating Expense:
Research and Development Expense	32,700,000	30,700,000	32,000,000.0
Selling and Administrative Expense	357,200,000	356,300,000	334,800,000
Total Operating Expense	389,900,000	387,000,000.0	366,800,000
Profit from Operations	71,800,000	58,000,000.0	33,000,000.0
Other Income (Expense):
Interest Income	3,300,000	3,000,000.0	2,400,000
Interest Expense	(21,100,000)	(23,300,000)	(25,400,000)
Net Foreign Currency Transaction Losses	(700,000)	(1,100,000)	(3,400,000)
Other Income (Expense), Net	700,000	(800,000)	(7,900,000)
Total Other Expense, Net	(17,800,000)	(22,200,000)	(34,300,000)
Profit (Loss) Before Income Taxes	54,000,000.0	35,800,000	(1,300,000)
Income Tax Expense	8,100,000	2,300,000	4,900,000
Net Earnings (Loss) Including Noncontrolling Interest	45,900,000	33,500,000	(6,200,000)
Net Earnings (Loss) Attributable to Noncontrolling Interest	100,000	100,000	0
Net Earnings (Loss) Attributable to Tennant Company	$ 45,800,000	$ 33,400,000	$ (6,200,000)
Net Earnings (Loss) Attributable to Tennant Company per Share:
Basic (in dollars per share)	$ 2.53	$ 1.86	$ (0.35)
Diluted (in dollars per share)	$ 2.48	$ 1.82	$ (0.35)
Weighted Average Shares Outstanding:
Basic (in shares)	18,118,486	17,940,438	17,695,390
Diluted (in shares)	18,453,145	18,338,569	17,695,390