CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Sales	$ 1,302,272	$ 1,132,892	$ 1,164,292
Cost of sales	820,748	718,313	718,316
Gross profit	481,524	414,579	445,976
Selling, general, and administrative expenses	363,717	315,586	315,468
Restructuring charges	2,614	2,150	0
Write-off of property, plant, and equipment	0	16,306	0
Operating profit	115,193	80,537	130,508
Pension settlement charge	5,735	2,162	0
Interest expense	20,911	7,483	5,405
Other income, net	(9,604)	(7,700)	(2,435)
Income before income tax expense	98,151	78,592	127,538
Income tax expense (benefit), net	24,896	(1,600)	45,424
Net earnings	73,255	80,192	82,114
Net earnings attributable to noncontrolling interests	7	29	30
Net earnings attributable to Knoll, Inc. stockholders	$ 73,248	$ 80,163	$ 82,084
Net earnings per common share attributable to Knoll, Inc. stockholders:
Basic (in dollars per share)	$ 1.51	$ 1.66	$ 1.71
Diluted (in dollars per share)	$ 1.49	$ 1.63	$ 1.68
Weighted-average number of common shares outstanding:
Basic (in shares)	48,657,015	48,422,558	48,093,294
Diluted (in shares)	49,218,193	49,160,492	48,919,108
Other comprehensive income (loss):
Unrealized loss on interest rate swap, net of tax	$ (1,250)	$ 0	$ 0
Pension and other post-employment liability adjustment, net of tax	2,645	(5,239)	(6,573)
Foreign currency translation adjustment	(13,140)	4,868	488
Foreign currency translation adjustment on long term intercompany notes	(8,114)	0	0
Total other comprehensive loss, net of tax	(19,859)	(371)	(6,085)
Total comprehensive income	53,396	79,821	76,029
Comprehensive income attributable to noncontrolling interests	7	29	30
Comprehensive income attributable to Knoll, Inc. stockholders	$ 53,389	$ 79,792	$ 75,999