EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net earnings attributable to Knoll, Inc. stockholders	$ 21.7	$ 13.1	$ 39.6	$ 28.4
Denominator:
Weighted-average shares of common stock outstanding—basic (in shares)	48,855,064	48,672,144	48,815,194	48,614,733
Potentially dilutive shares resulting from stock plans (in shares)	459,000	459,000	438,000	523,000
Denominator for diluted earnings per share - weighted-average shares (in shares)	49,314,364	49,131,106	49,252,546	49,137,528
Antidilutive equity awards not included in weighted-average common shares—diluted (in shares)	0	0	0	0
Net earnings per common share attributable to Knoll, Inc. stockholders:
Basic (in dollars per share)	$ 0.44	$ 0.27	$ 0.81	$ 0.58
Diluted (in dollars per share)	$ 0.44	$ 0.27	$ 0.80	$ 0.58