Business Combinations (Summary of Preliminary Allocation of Tangible and Identifiable Intangible Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jul. 14, 2017	Jun. 30, 2017
Preliminary Allocation
Goodwill	$ 118,554		$ 80,216
Avaya Networking
Preliminary Allocation
Accounts receivables, net		$ 18,112
Inventory		16,605
Other current assets		673
Property and equipment		3,768
Other long-term assets		2,568
Accounts payable and accrued expenses		(29,716)
Deferred revenue		(10,214)
Other liabilities		(6,608)
Total tangible assets acquired and liabilities assumed		(4,812)
Identifiable intangible assets		44,000
In-process research and development		2,300
Goodwill		38,338
Total intangible assets acquired		84,638
Total net assets acquired		$ 79,826