GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Segment	Sep. 30, 2014 USD ($)	Mar. 31, 2015 USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Number of operating segments | Segment			5
Goodwill	$ 1,702,705		$ 1,702,705		$ 197,445
Carrying value of intangible assets	1,102,717		1,102,717		50,180
Amortization expenses	9,843	$ 856	$ 10,652	$ 1,718
Weighted average useful life of acquired intangible assets			14 years 7 months
Acquired software and core technology | Included as cost of product revenue
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expenses	14,800	923	$ 15,600	1,900
Other acquired intangible assets | Included as operating expense
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expenses	9,800	$ 856	$ 10,700	$ 1,700
Developed and core technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets			11 years 6 months
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets			16 years 1 month
Trademarks and trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets			8 years 6 months
Leasehold interest
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets			5 years 7 months 6 days
Backlog
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets			2 years
Trade name
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	18,600		$ 18,600		18,600
Legacy
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	198,000		198,000		$ 197,400
Arbor Networks
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	534,700		534,700
Tektronix Communications
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	793,300		793,300
VSS
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	57,000		57,000
FNET
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 119,700		$ 119,700