SEGMENT INFORMATION - Average Assets for Segments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total assets	$ 5,235.1	$ 4,800.0
Operating segments | Bedding Products
Segment Reporting Information [Line Items]
Total assets	804.3	739.0
Operating segments | Specialized Products
Segment Reporting Information [Line Items]
Total assets	312.0	299.5
Operating segments | Furniture, Flooring & Textile Products
Segment Reporting Information [Line Items]
Total assets	368.9	348.6
Operating segments | Average current liabilities included in segment numbers above
Segment Reporting Information [Line Items]
Total assets	799.7	665.0
Unallocated assets
Segment Reporting Information [Line Items]
Total assets	2,726.8	2,759.1
Difference between average assets and period-end balance sheet
Segment Reporting Information [Line Items]
Total assets	$ 223.4	$ (11.2)