Quarterly Results of Operations (Unaudited) - Summary of Quarterly Financial Data (Parenthetical) (Details) - USD ($)		3 Months Ended							12 Months Ended
	May 31, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Data [Line Items]
Goodwill impairment charge		$ 0							$ 55,200,000
Debt Refinancing
Quarterly Financial Data [Line Items]
Restructuring charges						$ 38,700,000				$ 38,700,000
Treasury Lock
Quarterly Financial Data [Line Items]
Restructuring charges, after tax						$ 25,900,000
Restructuring charges, diluted per share						$ 0.28
Income tax benefit from stranded tax effects in accumulated OCI related to write-off of remaining treasury lock						$ 3,200,000
Wallula, Washington Mill
Quarterly Financial Data [Line Items]
Restructuring charges, after tax						$ 300,000	$ 2,300,000	$ 500,000
Restructuring charges, diluted per share						$ 0.00	$ 0.02	$ 0.01
Paper Reporting Unit
Quarterly Financial Data [Line Items]
Goodwill impairment charge	$ 55,200,000			$ 55,200,000
Non-cash goodwill impairment charge, after tax				$ 55,200,000
Non-cash goodwill impairment charge, diluted per share				$ 0.58
Packaging and Paper
Quarterly Financial Data [Line Items]
Restructuring charges		4,000,000.0	$ 3,300,000	$ 20,400,000					27,300,000
Restructuring charges, after tax		$ 3,000,000.0	$ 2,500,000	$ 15,300,000
Restructuring charges, diluted per share		$ 0.03	$ 0.03	$ 0.16
Packaging And Corporate And Other
Quarterly Financial Data [Line Items]
Restructuring charges						$ 400,000	$ 3,000,000.0	$ 600,000
Corrugated Products Facility Closure
Quarterly Financial Data [Line Items]
Restructuring charges					$ 400,000	300,000
Restructuring charges, after tax					$ 300,000	$ 200,000
Restructuring charges, diluted per share					$ 0.00	$ 0.00
COVID-19 | Packaging and Paper
Quarterly Financial Data [Line Items]
Incremental out-of-pocket costs				$ 6,100,000	$ 800,000				6,300,000
Incremental out-of-pocket costs, after tax				$ 4,600,000	$ 600,000
Incremental out-of-pocket costs, diluted per share				$ 0.05	$ 0.01
Hurricane Laura | DeRidder, Louisiana Mill
Quarterly Financial Data [Line Items]
Charges related to the impact of Hurricane Laura			$ 10,000,000.0						$ 10,000,000.0
Charges related to the impact of Hurricane Laura, after tax			$ 7,600,000
Charges related to the impact of Hurricane Laura, diluted per share			$ 0.08