QUARTERLY RESULTS (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Sales			$ 316,122	$ 291,256	$ 268,694	$ 256,820	$ 292,866	$ 292,097	$ 294,700	$ 284,629	$ 1,132,892	$ 1,164,292	$ 1,104,442
Gross profit			112,337	106,610	99,958	95,674	111,347	112,801	114,064	107,764	414,579	445,976	412,132
Net earnings			32,679	19,161	12,956	15,396	21,444	21,618	21,641	17,411	80,192	82,114	65,948
Net earnings attributable to Knoll, Inc. stockholders			$ 32,693	$ 19,132	$ 12,934	$ 15,404	$ 21,442	$ 21,607	$ 21,635	$ 17,400	$ 80,163	$ 82,084	$ 65,963
Earnings per share—Basic (in dollars per share)			$ 0.67	$ 0.39	$ 0.27	$ 0.32	$ 0.45	$ 0.45	$ 0.45	$ 0.36	$ 1.66	$ 1.71	$ 1.38
Earnings per share—Diluted (in dollars per share)			$ 0.67	$ 0.39	$ 0.26	$ 0.31	$ 0.44	$ 0.44	$ 0.44	$ 0.36	$ 1.63	$ 1.68	$ 1.36
Pension settlement charges	$ 2,200
Write-off of property, plant, and equipment	$ 16,300										$ 16,306	$ 0	$ 0
Restructuring charges		$ 2,200