Income Taxes (Narratives) (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2018	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
Income tax (benefit)	$ (5,270,000)	$ (1,617,000)	$ (3,868,000)	$ 58,000
State net operating loss	0	0	$ 0	0
Tax benefit, foreign	2,600,000
Tax benefit	4,700,000	$ 2,500,000		$ 2,500,000	$ 2,500,000
U.S. Federal tax rate		35.00%	21.00%	35.00%
Description of effective date of enacted tax rate implementation			Effective for tax years beginning on or after January 1, 2018.
Additional tax provision resulting corresponding reduction in valuation allowance	0		$ 0
Reduced valuation allowance	4,700,000		4,700,000
Unrecognized tax benefits	17,500,000		17,500,000
Unrecognized tax benefit future impact if recognized	17,500,000		$ 17,500,000
State
Operating Loss Carryforwards [Line Items]
Income tax examination, years under examination			2014 2015 2016
Enterasys, Zebra WLAN Business, Campus Fabric Business and Brocade Data Center Business
Operating Loss Carryforwards [Line Items]
Tax amortization deduction for capitalized goodwill	1,800,000		$ 4,100,000
Deferred tax liability, goodwill	$ 6,400,000		$ 6,400,000
Amortization period of intangible assets resulting from acquisitions			15 years
ASU 2016-16 | Ireland | Subsidiary
Operating Loss Carryforwards [Line Items]
Deferred tax asset relating to a transfer of certain assets to subsidiary						$ 3,700,000