EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net earnings attributable to Knoll, Inc. stockholders	$ 24,542	$ 20,323	$ 13,124	$ 15,259	$ 32,693	$ 19,132	$ 12,938	$ 15,404	$ 73,248	$ 80,163	$ 82,084
Denominator for basic earnings per share - weighted-average shares (in shares)									48,657,015	48,422,558	48,093,294
Potentially dilutive shares resulting from stock plans (in shares)									561,000	737,000	826,000
Denominator for diluted earnings per share - weighted-average shares (in shares)									49,218,193	49,160,492	48,919,108
Antidilutive equity awards not included in weighted-average common shares—diluted (in shares)									20,000	0	0
Basic (in dollars per share)	$ 0.50	$ 0.42	$ 0.27	$ 0.31	$ 0.67	$ 0.39	$ 0.27	$ 0.32	$ 1.51	$ 1.66	$ 1.71
Diluted (in dollars per share)	$ 0.50	$ 0.41	$ 0.27	$ 0.31	$ 0.67	$ 0.39	$ 0.26	$ 0.31	$ 1.49	$ 1.63	$ 1.68