Revenue Recognition - Disaggregation of Revenue (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) channel	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) product_category
Disaggregation of Revenue [Line Items]
Net sales	$ 871.3	$ 821.0	$ 722.8	$ 690.9	$ 676.1	$ 729.5	$ 659.9	$ 637.4	$ 3,106.0	$ 2,702.9	$ 2,700.6
Number of products sales channels | channel									2
Number of product categories | product_category											2
Royalty income, net of royalty expense									$ 0.0	0.0	$ 20.8
Shipping and handling included in net sales									19.3	13.6	11.3
United States
Disaggregation of Revenue [Line Items]
Net sales											1,954.2
Canada
Disaggregation of Revenue [Line Items]
Net sales											219.6
Bedding
Disaggregation of Revenue [Line Items]
Net sales										2,455.3	2,473.4
Other
Disaggregation of Revenue [Line Items]
Net sales										247.6	227.2
Operating Segments
Disaggregation of Revenue [Line Items]
Net sales									3,106.0	2,702.9
Operating Segments | Wholesale
Disaggregation of Revenue [Line Items]
Net sales									2,717.1	2,452.1
Operating Segments | Direct
Disaggregation of Revenue [Line Items]
Net sales									388.9	250.8
Operating Segments | United States
Disaggregation of Revenue [Line Items]
Net sales									2,312.3	1,928.9
Operating Segments | Canada
Disaggregation of Revenue [Line Items]
Net sales									221.0	207.3
Operating Segments | International
Disaggregation of Revenue [Line Items]
Net sales									572.7	566.7
Operating Segments | Bedding
Disaggregation of Revenue [Line Items]
Net sales									2,835.3	2,455.3
Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales									270.7	247.6
Operating Segments | North America
Disaggregation of Revenue [Line Items]
Net sales									2,533.3	2,136.2	2,173.8
Operating Segments | North America | Wholesale
Disaggregation of Revenue [Line Items]
Net sales									2,273.5	1,989.1
Operating Segments | North America | Direct
Disaggregation of Revenue [Line Items]
Net sales									259.8	147.1
Operating Segments | North America | United States
Disaggregation of Revenue [Line Items]
Net sales									2,312.3	1,928.9
Operating Segments | North America | Canada
Disaggregation of Revenue [Line Items]
Net sales									221.0	207.3
Operating Segments | North America | Bedding
Disaggregation of Revenue [Line Items]
Net sales									2,379.6	2,002.1	2,051.8
Operating Segments | North America | Other
Disaggregation of Revenue [Line Items]
Net sales									153.7	134.1	122.0
Operating Segments | International
Disaggregation of Revenue [Line Items]
Net sales									572.7	566.7	526.8
Operating Segments | International | Wholesale
Disaggregation of Revenue [Line Items]
Net sales									443.6	463.0
Operating Segments | International | Direct
Disaggregation of Revenue [Line Items]
Net sales									129.1	103.7
Operating Segments | International | International
Disaggregation of Revenue [Line Items]
Net sales									572.7	566.7
Operating Segments | International | Bedding
Disaggregation of Revenue [Line Items]
Net sales									455.7	453.2	421.6
Operating Segments | International | Other
Disaggregation of Revenue [Line Items]
Net sales									117.0	113.5	105.2
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Royalty income, net of royalty expense									$ 22.6	$ 20.9	$ 20.8