Employee Benefit Plans (Narratives) (Details)					3 Months Ended	12 Months Ended
	Nov. 07, 2019 shares	Nov. 08, 2018 shares	Feb. 01, 2016 shares	Aug. 27, 2014 shares	Mar. 31, 2019 Quarter $ / shares	Jun. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) Quarter $ / shares shares	Jun. 30, 2018 USD ($) Quarter $ / shares shares	Nov. 20, 2013 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding for options and awards						2,922,000	2,719,000
Total intrinsic value of options exercised | $						$ 600,000	$ 800,000	$ 6,300,000
Awards granted						637,000		0
Weighted-average estimated fair value of options granted (in dollars per share) | $ / shares						$ 3.52	$ 2.62
Total unrecognized compensation cost for unvested stock options | $						$ 1,800,000
Recognition period for compensation cost not yet recognized (in years, months, and days)						4 years 1 month 6 days
Stock options or Awards /units granted, grant date fair value | $ / shares						$ 6.42
Aggregate shares withheld upon vesting						1,300,000	1,300,000	1,000,000.0
Cash remitted to the appropriate taxing authorities | $						$ 8,000,000.0	$ 8,400,000	$ 11,300,000
Granted						7,151,000
Awards granted, shares						7,151,000
401(k) Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum annual contributions per employee | $						$ 19,500
Additional annual contribution per employee over age of 50 | $						$ 6,500
Employer matching contribution per dollar contributed by employee						0.50%
Maximum employer matching contribution of employee total compensation (percent)						2.50%
Matching contributions to the Plan | $						$ 3,200,000	4,200,000	3,300,000
Employer discretionary contributions | $						0	$ 0	0
Executive Officers and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted							900,000
Awards granted, shares							900,000
Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate fair value, as of the respective granted dates | $						$ 45,900,000	$ 30,000,000.0	$ 51,200,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognition period for compensation cost not yet recognized (in years, months, and days)						1 year 10 months 24 days
Share-based compensation arrangement by share-based payment award, award vesting percentage						The RSUs granted during the year ended June 30, 2020 vest from the original grant date as to one-third (1/3) on the one-year anniversary and one-twelfth (1/12) each quarter thereafter, subject to continued service to the Company.	The RSUs vest from the original grant date as to one-third (1/3) on the one-year anniversary and one-twelfth (1/12) each quarter thereafter, subject to continued service to the Company.
Stock options or Awards /units granted, grant date fair value | $						$ 34,400,000
Granted						600,000
Awards granted, shares						600,000
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options or Awards /units granted, grant date fair value | $ / shares							$ 6.40
Granted							600,000
Performance stock unit vesting, consecutive quarters | Quarter					2		2	2
Performance stock unit vesting, earnings per share threshold one | $ / shares					$ 0.32		$ 0.20	$ 0.20
Performance stock unit vesting, earnings per share threshold two | $ / shares					$ 0.20		$ 0.09
Awards granted, shares							600,000
Performance Shares | Executive Officers and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted							200,000
Awards granted, shares							200,000
Performance Shares | Other Vice President Level Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted							400,000
Awards granted, shares							400,000
Service-based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted, percentage								50.00%
Service-based Restricted Stock Units | Executive Officers and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted							700,000
Awards granted, shares							700,000
Market-Based Vesting | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options or Awards /units granted, grant date fair value | $ / shares								$ 10.61
Market-Based Vesting | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options or Awards /units granted, grant date fair value | $ / shares								$ 12.19
Certain Officers and Executive Vice Presidents | Performance Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted							851,700
Stock options/units vesting, stock trigger price | $ / shares							$ 10.00
Stock options vesting performance period							3 years
Stock options vesting, Threshold consecutive trading days from August 29, 2018 through August 31, 2021							30 days
Share-based compensation arrangement by share-based payment award, award vesting percentage						If the price hurdle is achieved, the PSOs will vest and will have expense recognized (ratably based upon the time elapsed between August 31, 2018 and the date the hurdle is met) and the remainder will vest and have expense recognized quarterly through August 31, 2021.
Stock options or Awards /units granted, grant date fair value | $ / shares						$ 2.62
Employees | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options/units vesting, stock trigger price | $ / shares							$ 10.00
Performance stock unit vesting, consecutive quarters | Quarter							2	2
Employees | Performance Shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance stock unit vesting, earnings per share | $ / shares							$ 0.20	$ 0.32
Execs | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted								1,200,000
Awards granted, shares								1,200,000
Execs | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted, percentage								50.00%
Execs | Market-Based Vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted								100,000
Awards granted, shares								100,000
Named Executive Officers | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted								600,000
Awards granted, shares								600,000
Chief Executive Officer | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted, percentage								40.00%
Chief Executive Officer | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted, percentage								60.00%
2013 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized shares for issuance									9,000,000.0
Shares subject to previously expired awards reinstated									12,700,000
Decrease in shares available for future grants for each Full Value Award awarded									150.00%
Additional authorized shares for issuance	7,000,000.0					7,000,000.0
Employee stock options and stock awards available for grant						13,100,000
Shares outstanding for options and awards						9,300,000
Contractual term						7 years
Enterasys Networks Inc. 2013 Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock options and stock awards available for grant						0
Shares outstanding for options and awards						600,000
Contractual term						7 years
Aerohive 2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock options and stock awards available for grant						0
Shares outstanding for options and awards						500,000
2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional authorized shares for issuance		7,500,000
Weighted-average estimated fair value of options granted (in dollars per share) | $ / shares						$ 1.90	$ 2.71	$ 3.25
Authorized shares for issuance				12,000,000.0		12,100,000
Maximum offering period per purchase period (in months)						6 months
Maximum of total compensation permitted to acquire shares (percent)				15.00%
Percent of fair market value for price per share to employees (percent)				85.00%
Shares issued under stock purchase plan						2,700,000	2,800,000
Maximum shares issuable for each purchase period			1,500,000	1,000,000.0