Financing Arrangements - 2026 Senior Notes - Additional Information (Detail) - USD ($)					3 Months Ended	12 Months Ended
		Oct. 28, 2019	Oct. 09, 2019	Jan. 02, 2018	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Oct. 01, 2015
Debt Instrument [Line Items]
Debt instrument interest rate						4.50%
Debt instrument maturity date						Nov. 15, 2026
Loss on debt extinguishment						$ 14,700,000	$ 0	$ 1,200,000
Payments of debt issuance costs				$ 65,300,000		4,300,000	$ 800,000	$ 65,800,000
Unamortized debt issuance costs						47,700,000
Senior Notes, Matures November 2026 [Member]
Debt Instrument [Line Items]
Debt instrument, aggregate principal amount			$ 300,000,000.0
Debt instrument interest rate			4.50%
Debt instrument, issue price percentage			100.00%
Debt instrument maturity date			Nov. 15, 2026
Debt instrument, interest payable commencement date			May 15, 2020
Payments of debt issuance costs			$ 4,800,000
Unamortized debt issuance costs						4,100,000
Senior Notes Payable	[1]					$ 295,900,000
Senior Notes, Matures October 2023 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate							6.38%		6.38%
Debt instrument maturity date							Oct. 01, 2023
Redemption of senior debt		$ 300,000,000.0
Debt redemption price percentage of principal amount		103.188%
Debt instrument, redemption description						On October 28, 2019, the Company used the net proceeds from the offering, together with cash on hand and available borrowings under the 2023 ABL (as defined below), to redeem all $300.0 million aggregate principal amount outstanding of the 2023 Senior Notes (as defined below) at a redemption price of 103.188%
Unamortized debt issuance costs		$ 5,100,000
Senior Notes Payable	[2]						$ 294,900,000
Refinancing the Existing 2023 Senior Notes with Issuance of 2026 Senior Notes [Member]
Debt Instrument [Line Items]
Loss on debt extinguishment					$ 14,700,000

[1] Interest rate of 4.50% as of September 30, 2020.

[2] Interest rate of 6.38% as of September 30, 2019.