Income Taxes (Narratives) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Dec. 22, 2017	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2014	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
Change in valuation allowance for fiscal year			$ 63,500	$ (8,500)
Federal tax net operating loss carry-forwards		$ 287,500	287,500
State tax net operating loss carry-forwards		156,400	156,400
Tax credit carry-forwards		67,364	67,364	54,745	$ 48,093
Amount of cumulative undistributed earnings to be reinvested indefinitely of non-U.S. subsidiaries		9,100	9,100
Deferred tax liability related to withholding taxes of certain foreign subsidiaries		551	551	$ 505	357
Unrecorded deferred tax liability for potential withholding tax of unrecognized foreign earnings		4,800	$ 4,800
Description of effective date of enacted tax rate implementation				effective for tax years beginning on or after January 1, 2018
Federal statutory income tax rate (percent)	35.00%		21.00%
Deferred intercompany gain		3,693	$ 3,693	$ 3,693
Additions resulting from the acquisition of Aerohive		75,000
Unrecognized tax benefits		23,897	23,897	17,168	17,506	$ 18,913
Unrecognized tax benefits that would affect the effective tax rate if recognized		500	500
Unrecognized tax benefit future impact if recognized		23,400	23,400
Estimated interest and penalties related to underpayment of income taxes, less than			$ 100	$ 100	$ 100
Enterasys Networks, Inc.
Operating Loss Carryforwards [Line Items]
Amortization period of intangible assets and goodwill resulting from acquisition							15 years
Zebra WLAN Business, Avaya Campus Fabric Business and Brocade Data Center Business
Operating Loss Carryforwards [Line Items]
Amortization period of intangible assets and goodwill resulting from acquisition						15 years
Aerohive Networks, Inc.
Operating Loss Carryforwards [Line Items]
Amortization period of intangible assets and goodwill resulting from acquisition			10 years
Enterasys Networks Inc, Zebra WLAN Business, Avaya Campus Fabric Business and Brocade Data Center Business
Operating Loss Carryforwards [Line Items]
Tax amortization deduction for capitalized goodwill			$ 7,600
MTS IRELAND
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		21,000	21,000
CITI MATCH AUSTRALIA
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		7,600	7,600
BRAZILIAN ENERGY EXCHANGE
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		700	700
Ireland | Subsidiary | ASU 2016-16
Operating Loss Carryforwards [Line Items]
Deferred intercompany gain								$ 7,200
Foreign
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		10,900	10,900
State
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		29,800	29,800
State | Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		900	900
State | Not Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		28,900	28,900
Federal
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		43,800	43,800
Federal | Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		$ 32,900	$ 32,900