Goodwill and Intangible Assets -Goodwill - Additional Information (Details) - USD ($)		3 Months Ended		12 Months Ended
	May 31, 2020	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill impairment charge		$ 0		$ 55,200,000
Discount rate utilized	0.09
Alternative Investment, Valuation Technique [Extensible List]	us-gaap:IncomeApproachValuationTechniqueMember
Alternative Investment, Measurement Input [Extensible List]	us-gaap:MeasurementInputDiscountRateMember
Goodwill		863,500,000		863,500,000	$ 918,700,000	$ 917,300,000
Packaging
Goodwill [Line Items]
Goodwill		863,500,000		863,500,000	863,500,000	862,100,000
Paper
Goodwill [Line Items]
Goodwill impairment charge				55,200,000
Goodwill		$ 0		$ 0	$ 55,200,000	$ 55,200,000
Recoverability test results recoverable percentage	100.00%
Paper Reporting Unit
Goodwill [Line Items]
Goodwill impairment charge	$ 55,200,000		$ 55,200,000