EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net earnings attributable to Knoll, Inc. stockholders	$ 18.0	$ 15.3
Weighted-average shares of common stock outstanding—basic (in shares)	48,774,883	48,556,686
Potentially dilutive shares resulting from stock plans (in shares)	415,000	648,000
Denominator for diluted earnings per share - weighted-average shares (in shares)	49,190,288	49,204,776
Antidilutive equity awards not included in weighted-average common shares—diluted (in shares)	110,000	1,000
Basic (in dollars per share)	$ 0.37	$ 0.31
Diluted (in dollars per share)	$ 0.37	$ 0.31