EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net earnings attributable to Knoll, Inc. stockholders	$ 13,124	$ 12,938	$ 28,383	$ 28,338
Basic earnings per share - weighted-average shares (in shares)	48,672,144	48,464,605	48,614,733	48,375,241
Potentially dilutive shares resulting from stock plans (in shares)	459,000	912,000	523,000	920,000
Diluted earnings per share - weighted-average shares (in shares)	49,131,106	49,376,506	49,137,528	49,294,525
Antidilutive equity awards not included in weighted-average common shares—diluted (in shares)	0	0	0	12,000
Basic (in dollars per share)	$ 0.27	$ 0.27	$ 0.58	$ 0.59
Diluted (in dollars per share)	$ 0.27	$ 0.26	$ 0.58	$ 0.57