REVENUE - Net Sales by Product Category (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue from External Customer [Line Items]
Total Sales	$ 332.8	$ 296.6
Office Segment
Revenue from External Customer [Line Items]
Total Sales	202.2	185.1
Lifestyle
Revenue from External Customer [Line Items]
Total Sales	130.6	111.5
Office Systems | Office Segment
Revenue from External Customer [Line Items]
Total Sales	106.3	104.0
Seating | Office Segment
Revenue from External Customer [Line Items]
Total Sales	30.9	31.0
Files and Storage | Office Segment
Revenue from External Customer [Line Items]
Total Sales	25.6	22.2
Ancillary | Office Segment
Revenue from External Customer [Line Items]
Total Sales	25.5	18.5
Other | Office Segment
Revenue from External Customer [Line Items]
Total Sales	13.9	9.4
Studio | Lifestyle
Revenue from External Customer [Line Items]
Total Sales	101.6	84.1
Coverings | Lifestyle
Revenue from External Customer [Line Items]
Total Sales	$ 29.0	$ 27.4