CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Sales	$ 1,132,892	$ 1,164,292	$ 1,104,442
Cost of sales	718,313	718,316	692,310
Gross profit	414,579	445,976	412,132
Selling, general, and administrative expenses	305,992	309,668	299,476
Restructuring charges	2,150	0	896
Write-off of property, plant, and equipment	16,306	0	0
Intangible asset impairment charge	0	0	10,650
Pension settlement charge	2,162	0	0
Operating profit	87,969	136,308	101,110
Interest expense	7,483	5,405	6,865
Other expense (income), net	1,894	3,365	(9,174)
Income before income tax expense	78,592	127,538	103,419
Income tax (benefit) expense, net	(1,600)	45,424	37,471
Net earnings	80,192	82,114	65,948
Net earnings (loss) attributable to noncontrolling interests	29	30	(15)
Net earnings attributable to Knoll, Inc. stockholders	$ 80,163	$ 82,084	$ 65,963
Net earnings per common share attributable to Knoll, Inc. stockholders:
Basic (in dollars per share)	$ 1.66	$ 1.71	$ 1.38
Diluted (in dollars per share)	$ 1.63	$ 1.68	$ 1.36
Weighted-average number of common shares outstanding:
Basic (in shares)	48,422,558	48,093,294	47,746,707
Diluted (in shares)	49,160,492	48,919,108	48,438,231
Other comprehensive income (loss):
Pension and other post-employment liability adjustment, net of tax	$ (5,239)	$ (6,573)	$ 11,945
Foreign currency translation adjustment	4,868	488	(16,581)
Total other comprehensive (loss), net of tax	(371)	(6,085)	(4,636)
Comprehensive income attributable to Knoll, Inc. stockholders	79,821	76,029	61,312
Comprehensive income (loss) attributable to noncontrolling interests	29	30	(15)
Comprehensive income attributable to Knoll, Inc. stockholders	$ 79,792	$ 75,999	$ 61,327