Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Tennant Company Shareholders' Equity	Noncontrolling Interest
Beginning balance at Dec. 31, 2015	$ 252,207	$ 6,654	$ 0	$ 293,682	$ (48,129)	$ 252,207	$ 0
Balance (in shares) at Dec. 31, 2015		17,744,381
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	46,614	$ 0	0	46,614	0	46,614	0
Other Comprehensive (Loss) Income	(1,794)	$ 0	0	0	(1,794)	(1,794)	0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares) (in shares)		190,443
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares)	4,010	$ 71	3,939	0	0	4,010	0
Share-Based Compensation	3,875	0	3,875	0	0	3,875	0
Dividends paid ($0.81, $0.84 and $0.85) per Common Share	(14,293)	0	0	(14,293)	0	(14,293)	0
Tax Benefit on Stock Plans	686	$ 0	686	0	0	686	0
Purchases of Common Stock (in shares)		(246,474)
Purchases of Common Stock	(12,762)	$ (92)	(4,847)	(7,823)	0	(12,762)	0
Balance (in shares) at Dec. 31, 2016		17,688,350
Ending balance at Dec. 31, 2016	278,543	$ 6,633	3,653	318,180	(49,923)	278,543	0
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	(6,205)	0	0	(6,195)	0	(6,195)	(10)
Other Comprehensive (Loss) Income	27,600	$ 0	0	0	27,600	27,600	0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares) (in shares)		192,827
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares)	5,617	$ 72	5,545	0	0	5,617	0
Share-Based Compensation	5,891	0	5,891	0	0	5,891	0
Dividends paid ($0.81, $0.84 and $0.85) per Common Share	(14,953)	0	0	(14,953)	0	(14,953)	0
Recognition of Noncontrolling Interests	2,028	0	0	0	0	0	2,028
Purchase of Noncontrolling Shareholder Interest	30	0	0	0	0	0	30
Other	$ 17	$ 0	0	0	0	0	17
Balance (in shares) at Dec. 31, 2017	17,881,177	17,881,177
Ending balance at Dec. 31, 2017	$ 298,474	$ 6,705	15,089	297,032	(22,323)	296,503	1,971
Increase (Decrease) in Stockholders' Equity
Net Earnings (Loss)	33,538	0	0	33,412	0	33,412	126
Other Comprehensive (Loss) Income	(14,871)	$ 0	0	0	(14,871)	(14,871)	0
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares) (in shares)		244,024
Issue Stock for Directors, Employee Benefit and Stock Plans, net of related tax withholdings (23,113, 16,990 and 9,598 shares)	5,239	$ 92	5,147	0	0	5,239	0
Share-Based Compensation	8,314	0	8,314	0	0	8,314	0
Dividends paid ($0.81, $0.84 and $0.85) per Common Share	(15,343)	0	0	(15,343)	0	(15,343)	0
Recognition of Noncontrolling Interests	(132)	0	0	0	0	0	(132)
Retained Earnings Adjustment	(1,168)	0	0	(1,168)	0	(1,168)	0
Other	$ (35)	$ 0	0	0	0	0	(35)
Balance (in shares) at Dec. 31, 2018	18,125,201	18,125,201
Ending balance at Dec. 31, 2018	$ 316,352	$ 6,797	$ 28,550	$ 316,269	$ (37,194)	$ 314,422	$ 1,930