Acquisitions - Additional Information (Details)			3 Months Ended		12 Months Ended
	Nov. 01, 2019 USD ($)	Nov. 19, 2018 USD ($) Employee	Sep. 30, 2020 USD ($) Employee	Jun. 29, 2019 USD ($) Employee	Sep. 30, 2020 USD ($) Employee	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Business Acquisition [Line Items]
Business combination, acquisition related costs					$ 8,600,000	$ 3,100,000	$ 500,000
Customer Lists
Business Acquisition [Line Items]
Acquired finite-lived intangible asset, weighted average useful life					10 years
Purchased Software
Business Acquisition [Line Items]
Acquired finite-lived intangible asset, weighted average useful life					11 years
Trademarks
Business Acquisition [Line Items]
Acquired finite-lived intangible asset, weighted average useful life					11 years
Onshape
Business Acquisition [Line Items]
Business combination, consideration transferred	$ 469,000,000
Cash acquired from acquisition	7,500,000
Goodwill, acquired	364,900,000				$ 364,910,000
Liabilities	4,100,000
Onshape | Customer Lists
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	56,800,000
Onshape | Purchased Software
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	47,300,000
Onshape | Trademarks
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	$ 3,600,000
Onshape | Maximum | Customer Lists
Business Acquisition [Line Items]
Acquired finite-lived intangible asset, weighted average useful life	10 years
Onshape | Maximum | Purchased Software
Business Acquisition [Line Items]
Acquired finite-lived intangible asset, weighted average useful life	16 years
Onshape | Maximum | Trademarks
Business Acquisition [Line Items]
Acquired finite-lived intangible asset, weighted average useful life	15 years
Frustum
Business Acquisition [Line Items]
Business combination, consideration transferred		$ 69,500,000
Cash acquired from acquisition		700,000
Goodwill, acquired		53,700,000				53,673,000
Liabilities		$ 2,100,000
Acquired finite-lived intangible asset, weighted average useful life		15 years
Entity number of employees | Employee		12
Frustum | Purchased Software
Business Acquisition [Line Items]
Finite-lived intangible assets acquired		$ 17,900,000
Other Acquisitions
Business Acquisition [Line Items]
Business combination, consideration transferred			$ 15,000,000.0	$ 17,300,000
Cash acquired from acquisition			100,000	300,000
Goodwill, acquired			12,300,000	12,600,000	12,262,000	$ 12,645,000
Liabilities			$ 1,400,000	$ 1,300,000	$ 1,400,000
Entity number of employees | Employee			20	95	20
Other Acquisitions | Customer Lists
Business Acquisition [Line Items]
Finite-lived intangible assets acquired			$ 700,000	$ 3,400,000
Acquired finite-lived intangible asset, weighted average useful life			10 years
Other Acquisitions | Purchased Software
Business Acquisition [Line Items]
Finite-lived intangible assets acquired			$ 3,400
Acquired finite-lived intangible asset, weighted average useful life			7 years