Net Sales - Disaggregation of Revenue (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) channel product_category	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Net sales	$ 3,676.9	$ 3,106.0	$ 2,702.9
Number of products sales channels | channel	2
Number of product categories | product_category	2
Shipping and handling included in net sales	$ 14.4	19.3	13.6
United States
Disaggregation of Revenue [Line Items]
Net sales			1,928.8
All Other
Disaggregation of Revenue [Line Items]
Net sales	790.3	793.9	774.1
Bedding
Disaggregation of Revenue [Line Items]
Net sales			2,455.3
Other
Disaggregation of Revenue [Line Items]
Net sales			247.6
Operating Segments
Disaggregation of Revenue [Line Items]
Net sales	3,676.9	3,106.0	2,702.9
Operating Segments | Wholesale
Disaggregation of Revenue [Line Items]
Net sales	3,185.8	2,717.1	2,452.1
Operating Segments | Direct
Disaggregation of Revenue [Line Items]
Net sales	491.1	388.9	250.8
Operating Segments | United States
Disaggregation of Revenue [Line Items]
Net sales	2,886.6	2,312.1	1,928.8
Operating Segments | Canada
Disaggregation of Revenue [Line Items]
Net sales	790.3	793.9
Operating Segments | All Other
Disaggregation of Revenue [Line Items]
Net sales			774.1
Operating Segments | Bedding
Disaggregation of Revenue [Line Items]
Net sales	3,353.8	2,837.0	2,455.3
Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	323.1	269.0	247.6
Operating Segments | North America Segment
Disaggregation of Revenue [Line Items]
Net sales	3,159.2	2,603.5	2,207.0
Operating Segments | North America Segment | Wholesale
Disaggregation of Revenue [Line Items]
Net sales	2,806.7	2,343.5	2,059.5
Operating Segments | North America Segment | Direct
Disaggregation of Revenue [Line Items]
Net sales	352.5	260.0	147.5
Operating Segments | North America Segment | United States
Disaggregation of Revenue [Line Items]
Net sales	2,886.6	2,312.1	1,928.8
Operating Segments | North America Segment | Canada
Disaggregation of Revenue [Line Items]
Net sales	272.6	291.4
Operating Segments | North America Segment | All Other
Disaggregation of Revenue [Line Items]
Net sales			278.2
Operating Segments | North America Segment | Bedding
Disaggregation of Revenue [Line Items]
Net sales	2,956.3	2,448.8	2,069.5
Operating Segments | North America Segment | Other
Disaggregation of Revenue [Line Items]
Net sales	202.9	154.7	137.5
Operating Segments | International Segment
Disaggregation of Revenue [Line Items]
Net sales	517.7	502.5	495.9
Operating Segments | International Segment | Wholesale
Disaggregation of Revenue [Line Items]
Net sales	379.1	373.6	392.6
Operating Segments | International Segment | Direct
Disaggregation of Revenue [Line Items]
Net sales	138.6	128.9	103.3
Operating Segments | International Segment | United States
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Operating Segments | International Segment | International
Disaggregation of Revenue [Line Items]
Net sales	517.7	502.5
Operating Segments | International Segment | All Other
Disaggregation of Revenue [Line Items]
Net sales			495.9
Operating Segments | International Segment | Bedding
Disaggregation of Revenue [Line Items]
Net sales	397.5	388.2	385.8
Operating Segments | International Segment | Other
Disaggregation of Revenue [Line Items]
Net sales	120.2	114.3	110.1
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Royalty income, net of royalty expense	$ 21.9	$ 22.6	$ 20.9