EQUITY - Schedule of Changes in Stockholders Equity and Noncontrolling Interest (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 358,729			$ 358,729
Net earnings		$ 20,323	$ 19,161	48,713	$ 47,513
Other comprehensive income		538	$ 5,737	(2,421)	$ 8,262
Shares issued under stock incentive plan				2
Shares issued to Board of Directors in lieu of cash				50
Stock-based compensation, net of forfeitures				6,738
Cash dividend ($0.15 per share)				(22,360)
Purchase of common stock (in shares)				(4,395)
Ending Balance		385,056		$ 385,056
Cash dividend (in dollars per share)				$ 0.15
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	493			$ 493
Shares issued under stock incentive plan				4
Purchase of common stock (in shares)				(2)
Ending Balance		495		495
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	54,455			54,455
Shares issued under stock incentive plan				(2)
Shares issued to Board of Directors in lieu of cash				50
Stock-based compensation, net of forfeitures				6,738
Purchase of common stock (in shares)				(4,393)
Ending Balance		56,848		56,848
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	347,304			347,304
Net earnings				48,706
Other comprehensive income				0
Cash dividend ($0.15 per share)				(22,360)
Ending Balance		379,900		379,900
Accumulated Other Comprehensive (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(43,774)			(43,774)
Other comprehensive income				(2,421)
Ending Balance		(52,445)		(52,445)
Total Knoll, Inc. Stockholders' Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	358,478			358,478
Net earnings				48,706
Other comprehensive income				(2,421)
Shares issued under stock incentive plan				2
Shares issued to Board of Directors in lieu of cash				50
Stock-based compensation, net of forfeitures				6,738
Cash dividend ($0.15 per share)				(22,360)
Purchase of common stock (in shares)				(4,395)
Ending Balance		384,798		384,798
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	251			251
Net earnings				7
Ending Balance		$ 258		$ 258
ASU 2018-02
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU 2018-02	(6,250)
ASU 2018-02 | Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU 2018-02	6,250
ASU 2018-02 | Accumulated Other Comprehensive (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU 2018-02	$ (6,250)