Business Combinations - Narrative (Details) - USD ($) $ in Thousands				12 Months Ended
	Jan. 22, 2021	Jan. 24, 2020	May 08, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition [Line Items]
Goodwill, Other Increase (Decrease)				$ 6,170	$ (6,024)
Volterra, Inc.
Business Acquisition [Line Items]
Total Purchase Price	$ 427,200
Identifiable Intangible Assets Useful Life	6 years 11 months 12 days
Volterra, Inc. | General and Administrative Expense
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs				9,500
Shape Security, Inc.
Business Acquisition [Line Items]
Total Purchase Price		$ 1,000,000
Transaction Costs		$ 23,200
Identifiable Intangible Assets Useful Life		6 years 6 months
Goodwill, Other Increase (Decrease)				$ (700)
Shape Security, Inc. | General and Administrative Expense
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs					$ 15,300
F5 Networks Acquisition of Nginx
Business Acquisition [Line Items]
Total Purchase Price			$ 643,200
Transaction Costs			$ 19,000
Identifiable Intangible Assets Useful Life			8 years 1 month 6 days
Tax Deductible Goodwill			$ 500,500
F5 Networks Acquisition of Nginx | General and Administrative Expense
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs						$ 1,000
Developed Technology Rights | Volterra, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life	7 years
Developed Technology Rights | Shape Security, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life		7 years
Developed Technology Rights | F5 Networks Acquisition of Nginx
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life			7 years
Customer Relationships | Volterra, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life	1 year
Customer Relationships | Shape Security, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life		4 years
Customer Relationships | F5 Networks Acquisition of Nginx
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life			15 years
Trade Names | Shape Security, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life		5 years
Trade Names | F5 Networks Acquisition of Nginx
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life			7 years