REVENUE - Net Sales by Product Category (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue from External Customer [Line Items]
Total Sales	$ 356.5	$ 327.7	$ 1,056.6	$ 947.6
Office Segment
Revenue from External Customer [Line Items]
Total Sales	219.1	200.6	644.5	580.3
Lifestyle Segment
Revenue from External Customer [Line Items]
Total Sales	137.4	127.1	412.1	367.3
Office Systems | Office Segment
Revenue from External Customer [Line Items]
Total Sales	111.2	112.3	332.3	322.3
Seating | Office Segment
Revenue from External Customer [Line Items]
Total Sales	32.3	30.0	97.8	95.1
Files and Storage | Office Segment
Revenue from External Customer [Line Items]
Total Sales	26.0	24.1	78.9	67.7
Ancillary | Office Segment
Revenue from External Customer [Line Items]
Total Sales	36.6	24.7	92.5	64.1
Other | Office Segment
Revenue from External Customer [Line Items]
Total Sales	13.0	9.5	43.0	31.1
Studio | Lifestyle Segment
Revenue from External Customer [Line Items]
Total Sales	108.7	98.4	323.5	283.4
Coverings | Lifestyle Segment
Revenue from External Customer [Line Items]
Total Sales	$ 28.7	$ 28.7	$ 88.6	$ 83.9