Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net Earnings (Loss) Including Noncontrolling Interest	$ 33,538	$ (6,205)	$ 46,614
Other Comprehensive (Loss) Income:
Foreign currency translation adjustments	(16,221)	28,356	109
Pension and retiree medical benefits	1,745	5,868	(2,248)
Cash flow hedge	1,341	(7,731)	(305)
Income Taxes:
Foreign currency translation adjustments	168	310	32
Pension and retiree medical benefits	(467)	(2,087)	504
Cash flow hedge	(1,437)	2,884	114
Total Other Comprehensive (Loss) Income, net of tax	(14,871)	27,600	(1,794)
Total Comprehensive Income Including Noncontrolling Interest	18,667	21,395	44,820
Comprehensive Income (Loss) Attributable to Noncontrolling Interest	126	(10)	0
Comprehensive Income Attributable to Tennant Company	$ 18,541	$ 21,405	$ 44,820