ACQUISITIONS - Narrative (Details) - USD ($)			3 Months Ended
	Oct. 07, 2015	Jul. 14, 2015	Jun. 30, 2016	Oct. 07, 2015	Jun. 30, 2015	Mar. 31, 2016	Jul. 13, 2015
Business Acquisition [Line Items]
Goodwill			$ 1,710,286,000			$ 1,709,369,000
Weighted average useful life of acquired intangible assets			14 years 7 months
Backlog
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			2 years
Trademarks and trade names
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			8 years 6 months
Leasehold interest
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			5 years 7 months 6 days
Arbor Networks
Business Acquisition [Line Items]
Goodwill			$ 534,900,000			534,800,000
Service assurance for service provider
Business Acquisition [Line Items]
Goodwill			795,500,000			794,400,000
Network visibility
Business Acquisition [Line Items]
Goodwill			57,000,000			57,000,000
Service assurance for enterprise
Business Acquisition [Line Items]
Goodwill			$ 125,100,000			125,100,000
Cash retention award | Vesting after August 4, 2015
Business Acquisition [Line Items]
Percent of cancelled Danaher equity awards replaced			50.00%
Restricted stock units | Vesting after August 4, 2015
Business Acquisition [Line Items]
Shares issued in business acquisition (in shares)			15,000,000
Percent of cancelled Danaher equity awards replaced			50.00%
Post combination compensation expense, Danaher equity awards | Vesting after August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense			$ 1,700,000
Contingently returnable consideration, cash retention award | Vesting after August 4, 2015 | Prepaid expenses and other current assets
Business Acquisition [Line Items]
Receivable from Danaher			8,400,000
Cash retention award | Vesting after August 4, 2015 | Accrued compensation
Business Acquisition [Line Items]
Cash liability			$ 9,700,000
Common stock
Business Acquisition [Line Items]
Share price (in dollars per share)							$ 36.89
Communications Business
Business Acquisition [Line Items]
Total equity consideration	$ 5,700,000	$ 2,299,911,000		$ 2,300,000,000
Increase (decrease) in accounts receivable	110,000	140,586,000		110,000
Increase in inventory	78,000	80,719,000		78,000
Decrease in prepaid expenses and other assets	(35,000)	(6,715,000)		(35,000)
Increase in property, plant and equipment	1,254,000	36,825,000		1,254,000
Increase (decrease) in accounts payable	8,000	21,311,000		8,000
Increase (decrease) in accrued expenses	176,000	12,916,000		176,000
Increase (decrease) in deferred revenue	65,000	187,882,000		65,000
Goodwill	$ 5,141,000	$ 1,507,847,000		$ 5,141,000		1,500,000,000
Weighted average useful life of acquired intangible assets			14 years 8 months
Revenues			$ 173,800,000
Net loss			3,700,000
Communications Business | General and administrative
Business Acquisition [Line Items]
Acquisition related costs			$ 0		$ 3,400,000
Communications Business | Developed technology
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			11 years 8 months 12 days
Communications Business | Customer relationships
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			16 years 3 months 18 days
Communications Business | Backlog
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			2 years
Communications Business | Trademarks and trade names
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			8 years 6 months
Communications Business | Leasehold interest
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			5 years 7 months 6 days
Communications Business | Arbor Networks
Business Acquisition [Line Items]
Goodwill						534,800,000
Communications Business | Service assurance for service provider
Business Acquisition [Line Items]
Goodwill						794,400,000
Communications Business | Network visibility
Business Acquisition [Line Items]
Goodwill						57,000,000
Communications Business | Service assurance for enterprise
Business Acquisition [Line Items]
Goodwill						$ 125,100,000
Communications Business | Common stock | Newco
Business Acquisition [Line Items]
Shares issued in business acquisition (in shares)		62,500,000