Acquisitions (Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands				12 Months Ended
	Jul. 06, 2021	Mar. 26, 2021	Dec. 13, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition [Line Items]
Cash				$ 19,108	$ 136,098	$ 0
Goodwill				225,522	$ 210,135	$ 153,422
Ctek
Business Acquisition [Line Items]
Cash	$ 12,012
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability	300			$ 300
Total consideration transferred	12,734
Fair value of net tangible assets acquired	397
Deferred tax liability on identifiable intangible assets	1,000
Goodwill	4,867
Total assets acquired and liabilities assumed	12,734
Haxiot
Business Acquisition [Line Items]
Cash		$ 7,100
Cash		7,096
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability		5,900
Total consideration transferred		12,996
Fair value of net tangible assets acquired		86
Deferred tax liability on identifiable intangible assets		1,145
Goodwill		8,605
Total assets acquired and liabilities assumed		12,996
Opengear
Business Acquisition [Line Items]
Cash			$ 148,058
Contingent consideration			5,100
Total consideration transferred			153,158
Fair value of net tangible assets acquired			18,096
Deferred tax liability on identifiable intangible assets			27,126
Goodwill			57,088
Total assets acquired and liabilities assumed			153,158
Customer Relationships | Ctek
Business Acquisition [Line Items]
Identifiable intangible assets	5,100
Customer Relationships | Haxiot
Business Acquisition [Line Items]
Identifiable intangible assets		3,900
Customer Relationships | Opengear
Business Acquisition [Line Items]
Identifiable intangible assets			79,000
Trademarks | Ctek
Business Acquisition [Line Items]
Identifiable intangible assets	70
Trademarks | Haxiot
Business Acquisition [Line Items]
Identifiable intangible assets		500
Trademarks | Opengear
Business Acquisition [Line Items]
Identifiable intangible assets			8,000
Purchased and Core Technology | Ctek
Business Acquisition [Line Items]
Identifiable intangible assets	$ 1,300
Purchased and Core Technology | Haxiot
Business Acquisition [Line Items]
Identifiable intangible assets		$ 1,050
Purchased and Core Technology | Opengear
Business Acquisition [Line Items]
Identifiable intangible assets			$ 18,100