Acquisitions (Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Dec. 13, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Goodwill		$ 210,135	$ 153,422	$ 154,535
Opengear
Business Acquisition [Line Items]
Cash	$ 148,058
Contingent consideration	5,100
Total consideration transferred	153,158
Fair value of net tangible assets acquired	19,217
Deferred tax liability on identifiable intangible assets	(27,401)
Goodwill	56,242
Total assets acquired and liabilities assumed	153,158
Customer Relationships | Opengear
Business Acquisition [Line Items]
Identifiable intangible assets	79,000
Purchased and Core Technology | Opengear
Business Acquisition [Line Items]
Identifiable intangible assets	18,100
Trademarks | Opengear
Business Acquisition [Line Items]
Identifiable intangible assets	$ 8,000