GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Segment	Dec. 31, 2014 USD ($)	Mar. 31, 2015 USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Number of operating segments | Segment			5
Goodwill	$ 1,693,876		$ 1,693,876		$ 197,445
Carrying value of intangible assets	1,075,532		1,075,532		50,180
Amortization expenses	11,249	$ 821	$ 21,901	$ 2,539
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	905	$ 30,300	2,800
Other acquired intangible assets | Included as operating expense
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expenses	11,300	$ 858	$ 22,000	$ 2,700
Developed and core technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets			11 years 6 months
Customer and distributor 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
Backlog
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets			2 years
Capitalized software
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets			4 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	197,500		197,500		$ 197,400
Arbor Networks
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	533,100		533,100
Tektronix Communications
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	784,800		784,800
VSS
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	57,000		57,000
FNET
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 121,500		$ 121,500