Restructuring and Other Charges - Additional Information (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 28, 2019 USD ($)	Sep. 30, 2020 USD ($) Employee	Sep. 30, 2019 USD ($)
Restructuring Cost And Reserve [Line Items]
Restructuring and other charges, net	$ (247)	$ (14,034)
Restructuring charges	(131)	(13,758)
Restructuring Reserve	6,752	27,606	$ 9,987	$ 31,086
Impairment and Accretion Exited Lease Facilities
Restructuring Cost And Reserve [Line Items]
Restructuring charges, exited facilities	(100)
Prior Headquarters Relocation Charge
Restructuring Cost And Reserve [Line Items]
Restructuring and other charges, net		(200)
Employee Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Restructuring charges	(160)	(13,631)
Restructuring Reserve	1,461	14,027	3,992	298
Employee Severance and Related Benefits | Restructuring Plan 2020
Restructuring Cost And Reserve [Line Items]
Restructuring charges	(200)		$ (30,800)
Number of employees | Employee			250
Facility Closures
Restructuring Cost And Reserve [Line Items]
Restructuring charges	29	(127)
Restructuring Reserve	5,291	$ 13,579	$ 5,995	$ 30,788
Facility Closures | Accrued Expenses and Other Current Liabilities
Restructuring Cost And Reserve [Line Items]
Restructuring Reserve	2,700
Facility Closures | Other Noncurrent Liabilities
Restructuring Cost And Reserve [Line Items]
Restructuring Reserve	$ 2,600