Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Net Sales	$ 1,123,511	$ 1,003,066	$ 808,572
Cost of Sales	678,478	603,253	456,977
Gross Profit	445,033	399,813	351,595
Operating Expense:
Research and Development Expense	30,739	32,013	34,738
Selling and Administrative Expense	356,316	334,782	248,592
Total Operating Expense	387,055	366,795	283,330
Profit from Operations	57,978	33,018	68,265
Other Income (Expense):
Interest Income	3,035	2,405	330
Interest Expense	(23,342)	(25,394)	(1,279)
Net Foreign Currency Transaction Losses	(1,100)	(3,387)	(392)
Other Expense, Net	(729)	(7,934)	(433)
Total Other Expense, Net	(22,136)	(34,310)	(1,774)
Profit (Loss) Before Income Taxes	35,842	(1,292)	66,491
Income Tax Expense	2,304	4,913	19,877
Net Earnings (Loss) Including Noncontrolling Interest	33,538	(6,205)	46,614
Net Earnings (Loss) Attributable to Noncontrolling Interest	126	(10)	0
Net Earnings (Loss) Attributable to Tennant Company	$ 33,412	$ (6,195)	$ 46,614
Net Earnings (Loss) Attributable to Tennant Company per Share:
Basic (in dollars per share)	$ 1.86	$ (0.35)	$ 2.66
Diluted (in dollars per share)	$ 1.82	$ (0.35)	$ 2.59
Weighted Average Shares Outstanding:
Basic (in shares)	17,940,438	17,695,390	17,523,267
Diluted (in shares)	18,338,569	17,695,390	17,976,183
Cash Dividends Declared per Common Share	$ 0.85	$ 0.84	$ 0.81