EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net earnings attributable to Knoll, Inc. stockholders	$ 17.5	$ 20.3	$ 57.1	$ 48.7
Denominator:
Weighted-average shares of common stock outstanding—basic (in shares)	48,873,186	48,694,438	48,834,737	48,641,595
Potentially dilutive shares resulting from stock plans (in shares)	701,000	537,000	525,000	548,000
Denominator for diluted earnings per share - weighted-average shares (in shares)	49,573,706	49,231,376	49,359,812	49,189,592
Anti-dilutive equity awards not included in weighted-average common shares—diluted (in shares)	0	1,000	0	0
Net earnings per common share attributable to Knoll, Inc. stockholders:
Basic (in dollars per share)	$ 0.36	$ 0.42	$ 1.17	$ 1.00
Diluted (in dollars per share)	$ 0.35	$ 0.41	$ 1.16	$ 0.99