Business Combinations (Summary of Preliminary Allocation of Tangible and Identifiable Intangible Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Oct. 27, 2017	Sep. 30, 2017	Jun. 30, 2017
Preliminary Allocation
Goodwill	$ 130,988			$ 80,216
Data Center Business
Preliminary Allocation
Accounts receivables		$ 33,488
Inventories		19,973
Prepaid expenses and other current assets		988
Property and equipment		29,160
Other assets		4,734
Accounts payable and accrued expenses		(15,850)
Deferred revenue		(33,519)
Total tangible assets acquired and liabilities assumed		38,974
Identifiable intangible assets		28,600
Goodwill		16,763
Total intangible assets acquired		45,363
Total net assets acquired		$ 84,337
Campus Fabric Business
Preliminary Allocation
Accounts receivables	18,295		$ 18,112
Inventories	15,545		16,605
Prepaid expenses and other current assets	673		673
Property and equipment	3,768		3,768
Other assets	5,311		2,568
Accounts payable and accrued expenses	(31,919)		(29,716)
Deferred revenue	(10,051)		(10,214)
Other long-term liabilities	(5,205)		(6,608)
Total tangible assets acquired and liabilities assumed	(3,583)		(4,812)
Identifiable intangible assets	46,900		44,000
In-process research and development	2,500		2,300
Goodwill	34,009		38,338
Total intangible assets acquired	83,409		84,638
Total net assets acquired	79,826		$ 79,826
Change during three months ended December 31, 2017
Adjustments, Accounts receivables	183
Adjustments, Inventory	(1,060)
Adjustments, Other assets	2,743
Adjustments, Accounts payable and accrued expenses	(2,203)
Adjustments, Deferred revenue	163
Adjustments, Other long-term liabilities	1,403
Adjustments, Net tangible assets acquired	1,229
Adjustments, Identifiable intangible assets	2,900
Adjustments, In-process research and development	200
Adjustments, Goodwill	(4,329)
Adjustments, Total intangible assets acquired	$ (1,229)