GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) reporting_unit	Sep. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Number of reporting units | reporting_unit				2
Goodwill	$ 1,712,962	$ 1,712,962		$ 1,712,962		$ 1,712,764
Carrying value of intangible assets	720,949	720,949		720,949		831,374
Impairment of intangible assets		0	$ 0	$ 35,871	$ 0
Weighted average useful life of acquired intangible assets				14 years 7 months
Developed and core technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets				11 years 3 months 15 days
Customer and distributor relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets				15 years 11 months
Trademarks and trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets				8 years 7 months
Capitalized software
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life of acquired intangible assets				3 years
Trade name
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	18,600	18,600		$ 18,600		18,600
Service Assurance
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	1,200,000	1,200,000		1,200,000		1,200,000
Security
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	555,400	$ 555,400		$ 555,400		$ 555,900
HNT tools business | Disposed of by Sale
Acquired Finite-Lived Intangible Assets [Line Items]
Decrease of intangible assets	$ 10,200