Leases (Details) ft² in Thousands	3 Months Ended	6 Months Ended
	Mar. 28, 2020 USD ($) ft²	Mar. 28, 2020 USD ($) ft²	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease not commenced, future lease payments	$ 2,200,000	$ 2,200,000
Boston Lease Square Feet | ft²	250	250
Boston lease year one payments	$ 11,000,000.0	$ 11,000,000.0
Boston lease per square foot annual increase	1	1
Boston lease annual increase	300,000	300,000
Boston lease building operating cost amount estimate year one	7,100,000	7,100,000
Boston lease leasehold improvement allowance	25,000,000	25,000,000
Boston lease leasehold improvement allowance per square foot	100	100
Lease Cost
Operating lease cost	10,386,000	19,143,000
Short-term lease cost	1,017,000	2,890,000
Variable lease cost	575,000	2,490,000
Sublease income	(1,013,000)	(2,025,000)
Total lease cost	10,965,000	22,498,000
Operating cash flows from operating leases	9,642,000	15,140,000
Right-of-use assets obtained in exchange for new operating lease liabilities(1)	(1,230,000)	4,151,000
Right-of-use assets obtained in exchange for new financing lease liabilities	$ 0	$ 1,500,000
Weighted-average remaining lease term - operating leases	12 years 3 months 25 days	12 years 3 months 25 days
Weighted-average remaining lease term - financing leases	5 years	5 years
Weighted-average discount rate - operating leases	5.50%	5.50%
Weighted-average discount rate - financing leases	3.00%	3.00%
Operating Lease (ASC 842)
Remainder of 2020	$ 22,462,000	$ 22,462,000
2021	42,670,000	42,670,000
2022	28,457,000	28,457,000
2023	21,174,000	21,174,000
2024	17,757,000	17,757,000
Thereafter	186,554,000	186,554,000
Total future lease payments	319,074,000	319,074,000
Less: imputed interest	(94,916,000)	(94,916,000)
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
Operating right-of-use lease assets	157,016,000	157,016,000	0
Operating Lease, Liability	$ 224,158,000	$ 224,158,000
Minimum [Member]
Operating Lease (ASC 842)
Operating leases not yet commenced, term	3 years	3 years
Maximum [Member]
Operating Lease (ASC 842)
Operating leases not yet commenced, term	5 years	5 years
Facility closures and related costs
Lessee, Lease, Description [Line Items]
Operating Lease Liability, Net. Restructured Facilities	$ 17,100,000	$ 17,100,000	$ 16,500,000
Lease Cost
Operating cash flows from operating leases	2,100,000	4,500,000
Operating Leases (ASC 840)
Operating right-of-use lease assets	4,500,000	4,500,000
Operating Lease, Liability	21,600,000	21,600,000
Sublease Income Committed [Member]
Operating Leases (ASC 840)
Sublease Income Assumed	3,300,000	3,300,000
Sublease Income Estimated Uncommitted [Member]
Operating Leases (ASC 840)
Sublease Income Assumed	1,200,000	1,200,000
Onshape [Member]
Operating Leases (ASC 840)
Operating Lease, Impairment Loss	700,000
Operating Lease Short Term Lease Obligation [Member] | Facility closures and related costs
Operating Leases (ASC 840)
Operating Lease, Liability	13,300,000	13,300,000
Operating Lease Long Term Lease Obligation [Member] | Facility closures and related costs
Operating Leases (ASC 840)
Operating Lease, Liability	8,300,000	$ 8,300,000
Prior Headquarters [Member] | Facility closures and related costs
Operating Leases (ASC 840)
Operating Lease, Impairment Loss	$ 4,000,000.0