Income Taxes (Narratives) (Details) - USD ($)		3 Months Ended	6 Months Ended		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2014	Jun. 30, 2015
Operating Loss Carryforwards [Line Items]
Change in valuation allowance for fiscal year					$ (34,200,000)	$ 15,500,000
Federal tax net operating loss carry-forwards			$ 185,600,000		185,600,000
State tax net operating loss carry-forwards			54,400,000		54,400,000
Tax credit carry-forwards			48,093,000		48,093,000	34,444,000	$ 32,730,000
Amount of cumulative undistributed earnings to be reinvested indefinitely of non-U.S. subsidiaries			14,100,000		14,100,000
Deferred tax liability related to withholding taxes of certain foreign subsidiaries			357,000		357,000	321,000	235,000
Unrecorded deferred tax liability for potential withholding tax of unrecognized foreign earnings			$ 2,700,000		$ 2,700,000
Description of effective date of enacted tax rate implementation					Effective for tax years beginning on or after January 1, 2018.
Tax benefit					$ 2,500,000
U.S. Federal tax rate			21.00%	35.00%	28.00%
Tax benefit		$ 2,500,000			$ 13,061,000	(909,000)	11,209,000
Additional tax provision resulting corresponding reduction in valuation allowance			$ 0		0
Unrecognized tax benefits			17,506,000		17,506,000	18,913,000	11,653,000		$ 11,359,000
Unrecognized tax benefit future impact if recognized			17,500,000		17,500,000
Estimated interest and penalties related to underpayment of income taxes, less than					$ 100,000	$ 100,000	$ 100,000
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
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					$ 7,500,000
Fiscal 2018
Operating Loss Carryforwards [Line Items]
U.S. Federal tax rate	28.00%
MTS IRELAND
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards			37,500,000		37,500,000
CITI MATCH AUSTRALIA
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards			9,000,000		9,000,000
BRAZILIAN ENERGY EXCHANGE
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards			700,000		700,000
Foreign
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards			10,600,000		10,600,000
State
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards			18,800,000		18,800,000
Income tax examination, years under examination						2014 2015 2016
State | Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards			900,000		900,000
State | Not Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards			17,900,000		17,900,000
Federal
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards			33,200,000		33,200,000
Federal | Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards			$ 22,600,000		$ 22,600,000