REVENUE - Net Sales by Product Category (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue from External Customer [Line Items]
Total Sales	$ 367.3	$ 323.4	$ 700.1	$ 619.9
Office Segment
Revenue from External Customer [Line Items]
Total Sales	223.2	194.6	425.4	379.7
Lifestyle
Revenue from External Customer [Line Items]
Total Sales	144.1	128.8	274.7	240.2
Office Systems | Office Segment
Revenue from External Customer [Line Items]
Total Sales	114.8	106.0	221.1	210.0
Seating | Office Segment
Revenue from External Customer [Line Items]
Total Sales	34.6	34.1	65.5	65.1
Files and Storage | Office Segment
Revenue from External Customer [Line Items]
Total Sales	27.4	21.4	52.9	43.6
Ancillary | Office Segment
Revenue from External Customer [Line Items]
Total Sales	30.3	20.9	55.9	39.4
Other | Office Segment
Revenue from External Customer [Line Items]
Total Sales	16.1	12.2	30.0	21.6
Studio | Lifestyle
Revenue from External Customer [Line Items]
Total Sales	113.3	101.0	214.8	185.0
Coverings | Lifestyle
Revenue from External Customer [Line Items]
Total Sales	$ 30.8	$ 27.8	$ 59.9	$ 55.2