Restructuring and Other Charges (Additional Information) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 30, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 30, 2019 USD ($) employee	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 26,980	$ 114	$ 45,473	$ 219
Free rent and estimated sublease income new headquarters	30,000		30,000
Estimated undiscounted cash flows old headquarters	34,000		34,000
Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Assumed Sublease Income	13,900		13,900
Committed Sublease Income	1,000		1,000
Uncommitted Sublease Income	11,300		11,300
Accrued Expenses and Other Current Liabilities [Member] | Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	12,400	1,900	12,400	1,900
Other Noncurrent Liabilities [Member] | Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	18,900	1,400	18,900	1,400
Restructuring Plan 2019 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			$ 16,000
Restructuring and Related Cost, Number of Positions Eliminated | employee			240
Prior Year Plans [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			$ 300
2016 and 2019 Restructuring Plans [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			42,971
Restructuring Reserve	32,238		32,238		$ 2,415
2016 and 2019 Restructuring Plans [Member] | Employee severance and related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			16,034
Restructuring Reserve	955		955		0
2016 and 2019 Restructuring Plans [Member] | Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			26,937
Restructuring Reserve	31,283		31,283		2,415
Gross Lease Commitments	43,600		43,600
Restructuring Plan 2016 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net				(734)
Restructuring Reserve		3,559		3,559		$ 6,244
Restructuring Plan 2016 [Member] | Employee severance and related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net				(395)
Restructuring Reserve		243		243		1,736
Restructuring Plan 2016 [Member] | Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net				(339)
Restructuring Reserve		$ 3,316		$ 3,316	$ 2,400	$ 4,508
Prior Headquarters [Member] | Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	$ 26,700		26,700
Depreciation			1,900
Payments for Rent			$ 600