Leases (Details) ft² in Thousands	3 Months Ended
	Dec. 28, 2019 USD ($) ft²	Sep. 30, 2019 USD ($)
Leases [Abstract]
Boston Lease Square Feet | ft²	250
Boston lease year one payments	$ 11,000,000.0
Boston lease per square foot annual increase	1
Boston lease annual increase	300,000
Boston lease building operating cost amount estimate year one	7,100,000
Boston lease leasehold improvement allowance	25,000,000
Boston lease leasehold improvement allowance per square foot	100
Lease Cost
Operating lease cost	8,757,000
Short-term lease cost	1,874,000
Variable lease cost	1,914,000
Sublease income	(1,012,000)
Total lease cost	11,533,000
Operating cash flows from operating leases	5,498,000
Right-of-use assets obtained in exchange for new operating lease liabilities	5,380,000
Right-of-use assets obtained in exchange for new financing lease liabilities	$ 1,500,000
Weighted-average remaining lease term - operating leases	12 years 4 months 24 days
Weighted-average remaining lease term - financing leases	5 years
Weighted-average discount rate - operating leases	5.60%
Weighted-average discount rate - financing leases	3.00%
Operating Lease (ASC 842)
Remainder of 2020	$ 21,863,000
2021	30,858,000
2022	22,045,000
2023	18,939,000
2024	17,965,000
Thereafter	185,847,000
Total future lease payments	297,517,000
Less: imputed interest	(72,254,000)
Total	225,263,000
Operating leases not yet commenced	3,800,000
Finance leases not yet commenced	$ 1,500,000
Operating leases not yet commenced, term	7 years
Finance leases not yet commenced, term	5 years
Operating Leases (ASC 840)
2020		$ 31,868,000
2021		33,094,000
2022		25,624,000
2023		19,279,000
2024		16,909,000
Thereafter		186,037,000
Total minimum lease payments		$ 312,811,000