Separate Financial Information of Guarantor Subsidiaries Statements of Earnings (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Net Sales	$ 294,800,000	$ 280,700,000	$ 299,700,000	$ 262,500,000	$ 285,200,000	$ 273,300,000	$ 292,200,000	$ 272,800,000	$ 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	118,600,000	114,000,000.0	120,800,000	108,200,000	112,200,000	106,500,000	117,200,000	109,100,000	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 and Expenses [Abstract]
Equity in Earnings of Affiliates									0	0	0
Interest Expense, Net									(17,800,000)	(20,300,000)	(23,000,000.0)
Intercompany Interest Income (Expense)									0	0	0
Net Foreign Currency Transaction Losses									(700,000)	(1,100,000)	(3,400,000)
Other (Expense) Income, 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 (Benefit)									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 Attributable to Noncontrolling Interest									100,000	100,000	0
Net Earnings (Loss) Attributable to Tennant Company	$ 10,900,000	$ 14,600,000	$ 14,800,000	$ 5,400,000	$ 7,700,000	$ 9,700,000	$ 12,700,000	$ 3,300,000	45,800,000	33,400,000	(6,200,000)
Parent Company
Debt Instrument [Line Items]
Net Sales									529,600,000	494,400,000	454,700,000
Cost of Sales									347,200,000	336,400,000	311,900,000
Gross Profit									182,400,000	158,000,000.0	142,800,000
Operating Expense:
Research and Development Expense									25,900,000	24,500,000	27,200,000
Selling and Administrative Expense									117,800,000	116,500,000	110,400,000
Total Operating Expense									143,700,000	141,000,000.0	137,600,000
Profit from Operations									38,700,000	17,000,000.0	5,200,000
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									21,000,000.0	27,400,000	12,700,000
Interest Expense, Net									(17,400,000)	(20,500,000)	(22,700,000)
Intercompany Interest Income (Expense)									13,900,000	14,600,000	12,500,000
Net Foreign Currency Transaction Losses									300,000	(400,000)	900,000
Other (Expense) Income, Net									(2,200,000)	(2,300,000)	(9,900,000)
Total Other Expense, Net									15,600,000	18,800,000	(6,500,000)
Profit (Loss) Before Income Taxes									54,300,000	35,800,000	(1,300,000)
Income Tax Expense (Benefit)									8,400,000	2,300,000	4,900,000
Net Earnings (Loss) Including Noncontrolling Interest									45,900,000	33,500,000	(6,200,000)
Net Earnings Attributable to Noncontrolling Interest									100,000	100,000
Net Earnings (Loss) Attributable to Tennant Company									45,800,000	33,400,000	(6,200,000)
Guarantor Subsidiaries
Debt Instrument [Line Items]
Net Sales									666,200,000	634,300,000	594,400,000
Cost of Sales									563,000,000.0	533,800,000	489,000,000.0
Gross Profit									103,200,000	100,500,000	105,400,000
Operating Expense:
Research and Development Expense									1,100,000	1,000,000.0	300,000
Selling and Administrative Expense									76,400,000	76,600,000	78,500,000
Total Operating Expense									77,500,000	77,600,000	78,800,000
Profit from Operations									25,700,000	22,900,000	26,600,000
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									2,000,000.0	2,200,000	2,000,000.0
Interest Expense, Net									0	0	0
Intercompany Interest Income (Expense)									(5,700,000)	(5,800,000)	(5,800,000)
Net Foreign Currency Transaction Losses									0	0	0
Other (Expense) Income, Net									(1,300,000)	(2,400,000)	(700,000)
Total Other Expense, Net									(5,000,000.0)	(6,000,000.0)	(4,500,000)
Profit (Loss) Before Income Taxes									20,700,000	16,900,000	22,100,000
Income Tax Expense (Benefit)									4,900,000	4,000,000.0	8,100,000
Net Earnings (Loss) Including Noncontrolling Interest									15,800,000	12,900,000	14,000,000.0
Net Earnings Attributable to Noncontrolling Interest									0	0
Net Earnings (Loss) Attributable to Tennant Company									15,800,000	12,900,000	14,000,000.0
Non-Guarantor Subsidiaries
Debt Instrument [Line Items]
Net Sales									554,600,000	570,600,000	471,600,000
Cost of Sales									376,100,000	383,000,000.0	321,800,000
Gross Profit									178,500,000	187,600,000	149,800,000
Operating Expense:
Research and Development Expense									5,700,000	5,200,000	4,500,000
Selling and Administrative Expense									163,000,000.0	161,900,000	145,900,000
Total Operating Expense									168,700,000	167,100,000	150,400,000
Profit from Operations									9,800,000	20,500,000	(600,000)
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									2,800,000	5,400,000	28,900,000
Interest Expense, Net									(400,000)	200,000	(300,000)
Intercompany Interest Income (Expense)									(8,200,000)	(8,800,000)	(6,700,000)
Net Foreign Currency Transaction Losses									(1,000,000.0)	(700,000)	(4,300,000)
Other (Expense) Income, Net									4,300,000	2,800,000	2,800,000
Total Other Expense, Net									(2,500,000)	(1,100,000)	20,400,000
Profit (Loss) Before Income Taxes									7,300,000	19,400,000	19,800,000
Income Tax Expense (Benefit)									(1,200,000)	400,000	(100,000)
Net Earnings (Loss) Including Noncontrolling Interest									8,500,000	19,000,000.0	19,900,000
Net Earnings Attributable to Noncontrolling Interest									100,000	100,000
Net Earnings (Loss) Attributable to Tennant Company									8,400,000	18,900,000	19,900,000
Eliminations
Debt Instrument [Line Items]
Net Sales									(612,800,000)	(575,800,000)	(517,600,000)
Cost of Sales									(610,400,000)	(574,700,000)	(519,400,000)
Gross Profit									(2,400,000)	(1,100,000)	1,800,000
Operating Expense:
Research and Development Expense									0	0	0
Selling and Administrative Expense									0	1,300,000	0
Total Operating Expense									0	1,300,000	0
Profit from Operations									(2,400,000)	(2,400,000)	1,800,000
Other Income and Expenses [Abstract]
Equity in Earnings of Affiliates									(25,800,000)	(35,000,000.0)	(43,600,000)
Interest Expense, Net									0	0	0
Intercompany Interest Income (Expense)									0	0	0
Net Foreign Currency Transaction Losses									0	0	0
Other (Expense) Income, Net									(100,000)	1,100,000	(100,000)
Total Other Expense, Net									(25,900,000)	(33,900,000)	(43,700,000)
Profit (Loss) Before Income Taxes									(28,300,000)	(36,300,000)	(41,900,000)
Income Tax Expense (Benefit)									(4,000,000.0)	(4,400,000)	(8,000,000.0)
Net Earnings (Loss) Including Noncontrolling Interest									(24,300,000)	(31,900,000)	(33,900,000)
Net Earnings Attributable to Noncontrolling Interest									(100,000)	(100,000)
Net Earnings (Loss) Attributable to Tennant Company									$ (24,200,000)	$ (31,800,000)	$ (33,900,000)