EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net earnings attributable to Knoll, Inc. stockholders	$ 20,323	$ 19,132	$ 48,706	$ 47,470
Denominator:
Basic earnings per share - weighted-average shares (in shares)	48,694,438	48,468,480	48,641,595	48,406,659
Potentially dilutive shares resulting from stock plans (in shares)	537,000	511,000	548,000	761,000
Diluted earnings per share - weighted-average shares (in shares)	49,231,376	48,979,182	49,189,592	49,167,856
Antidilutive equity awards not included in weighted-average common shares—diluted (in shares)	1,000	34,000	0	15,000
Net earnings per common share attributable to Knoll, Inc. stockholders:
Basic (in dollars per share)	$ 0.42	$ 0.39	$ 1.00	$ 0.98
Diluted (in dollars per share)	$ 0.41	$ 0.39	$ 0.99	$ 0.96