Income Taxes (Narratives) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2014	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2016
Operating Loss Carryforwards [Line Items]
Change in valuation allowance for fiscal year		$ (8,500)	$ (34,200)
Federal tax net operating loss carry-forwards		126,600
State tax net operating loss carry-forwards		56,700
Tax credit carry-forwards		54,745	48,093	$ 34,444
Amount of cumulative undistributed earnings to be reinvested indefinitely of non-U.S. subsidiaries		6,800
Deferred tax liability related to withholding taxes of certain foreign subsidiaries		505	$ 357	321
Unrecorded deferred tax liability for potential withholding tax of unrecognized foreign earnings		$ 3,400
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%	28.00%
Tax benefit			$ 2,500
Reduced valuation allowance						$ 4,700
Deferred intercompany gain		$ 3,693
Unrecognized tax benefits		17,168	17,506	18,913				$ 11,653
Unrecognized tax benefit future impact if recognized		17,200
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
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		$ 7,700
MTS IRELAND
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		36,900
CITI MATCH AUSTRALIA
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		7,900
BRAZILIAN ENERGY EXCHANGE
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards		400
Ireland | Subsidiary | ASU 2016-16
Operating Loss Carryforwards [Line Items]
Deferred intercompany gain							$ 3,700
Foreign
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		10,700
State
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		22,100
State | Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		900
State | Not Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		21,200
Federal
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		37,300
Federal | Subject To Expiration
Operating Loss Carryforwards [Line Items]
Tax credit carry-forwards		$ 26,600