Segment Information - Additional Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Insurance proceeds received, net cash used for investing activities			$ 1.4	$ 8.8
Corrugated Packaging [Member] | Hurricane Michael [Member]
Segment Reporting Information [Line Items]
Insurance proceeds received	$ 32.3
Deferred insurance proceeds	2.8
Deferred insurance proceeds recognized in cost of goods sold			2.8
Insurance proceeds from business interruption recoveries	11.7			30.0
Insurance proceeds for direct costs and property damage	20.6			50.0
Insurance proceeds received, net cash provided by operating activities			30.9	71.2
Insurance proceeds received, net cash used for investing activities			$ 1.4	8.8
Corrugated Packaging [Member] | Hurricane Michael [Member] | Cost of Goods Sold [Member]
Segment Reporting Information [Line Items]
Insurance proceeds received		$ 60.0		$ 80.0
Reduction of cost of goods sold	$ 29.5