EQUITY - Schedule of Change in Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 392.8	$ 386.5	$ 366.4	$ 358.8	$ 386.5	$ 358.8
Net earnings	21.7	18.0	13.1	15.3	39.6	28.4
Other comprehensive (loss) income	0.0	(3.6)	(2.2)	(0.8)	(3.6)	(2.9)
Stock-based compensation, net of forfeitures	2.4	2.2	2.1	2.4
Cash dividend	(8.6)	(7.5)	(7.9)	(7.3)
Purchase of common stock		(3.0)	(2.4)	(2.0)
Other	0.1	0.2
Ending Balance	$ 408.4	$ 392.8	$ 369.1	$ 366.4	408.4	369.1
Cash dividends (in dollars per share)	$ 0.17	$ 0.15	$ 0.15	$ 0.15
Purchase of common stock, shares (in shares)		141,738		95,412
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 0.5	$ 0.5	$ 0.5	$ 0.5	0.5	0.5
Ending Balance	0.5	0.5	0.5	0.5	0.5	0.5
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	58.4	58.8	54.9	54.5	58.8	54.5
Stock-based compensation, net of forfeitures	2.4	2.2	2.1	2.4
Purchase of common stock		(3.0)	(2.4)	(2.0)
Other	0.1	0.4
Ending Balance	60.9	58.4	54.6	54.9	60.9	54.6
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	405.9	395.4	361.5	347.3	395.4	347.3
Net earnings	21.7	18.0	13.1	15.3
Cash dividend	(8.6)	(7.5)	(7.9)	(7.3)
Ending Balance	419.0	405.9	366.7	361.5	419.0	366.7
Retained Earnings | ASU 2018-02
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU 2018-02				6.3
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(72.0)	(68.4)	(50.8)	(43.8)	(68.4)	(43.8)
Other comprehensive (loss) income		(3.6)	(2.2)	(0.8)
Ending Balance	(72.0)	(72.0)	(53.0)	(50.8)	(72.0)	(53.0)
Accumulated Other Comprehensive Income (Loss) | ASU 2018-02
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU 2018-02				(6.3)
Total Knoll, Inc. Stockholders' Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	392.8	386.3	366.1	358.5	386.3	358.5
Net earnings	21.7	18.0	13.1	15.3
Other comprehensive (loss) income	0.0	(3.6)	(2.2)	(0.8)
Stock-based compensation, net of forfeitures	2.4	2.2	2.1	2.4
Cash dividend	(8.6)	(7.5)	(7.9)	(7.3)
Purchase of common stock		(3.0)	(2.4)	(2.0)
Other	0.1	0.4
Ending Balance	408.4	392.8	368.8	366.1	408.4	368.8
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	0.0	0.2	0.3	0.3	0.2	0.3
Net earnings				0.0
Other		(0.2)
Ending Balance	$ 0.0	$ 0.0	$ 0.3	$ 0.3	$ 0.0	$ 0.3