ACQUISITIONS - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions				3 Months Ended			6 Months Ended
	Aug. 19, 2016	Oct. 07, 2015	Jul. 14, 2015	Sep. 30, 2016	Oct. 07, 2015	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Aug. 20, 2017	Mar. 31, 2016	Jul. 13, 2015
Business Acquisition [Line Items]
Contingent purchase consideration				$ 9,282,000			$ 9,282,000			$ 7,293,000
Goodwill				1,714,539,000			$ 1,714,539,000			1,709,369,000
Weighted average useful life of acquired intangible assets							14 years 7 months
Increase in goodwill							$ 2,817,000
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
Service Assurance
Business Acquisition [Line Items]
Goodwill				1,200,000,000			$ 1,200,000,000			1,200,000,000
Security
Business Acquisition [Line Items]
Goodwill				$ 548,500,000			$ 548,500,000			547,400,000
Cash retention award | Vesting after August 4, 2015
Business Acquisition [Line Items]
Percent of cancelled Danaher equity awards replaced				50.00%			50.00%
Restricted stock units | Vesting after August 4, 2015
Business Acquisition [Line Items]
Percent of cancelled Danaher equity awards replaced				50.00%			50.00%
Business acquisition, equity interest issued, value				$ 15,000,000			$ 15,000,000
Post combination compensation expense, Danaher equity awards | Vesting July 14, 2015 through August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense						$ 6,500,000		$ 6,500,000
Post combination compensation expense, Danaher equity awards | Vesting after August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense				2,600,000		2,600,000	4,300,000	2,600,000
Contingently returnable consideration, cash retention award | Vesting after August 4, 2015 | Prepaid expenses and other current assets
Business Acquisition [Line Items]
Receivable from Danaher				11,600,000			11,600,000
Contingently returnable consideration, cash retention award | Vesting after August 4, 2015 | Accounts payable
Business Acquisition [Line Items]
Contingent purchase consideration				$ 3,900,000			$ 3,900,000
Post combination compensation expense, Danaher bonus
Business Acquisition [Line Items]
Post combination compensation expense						4,100,000		4,100,000
Post combination compensation expense, Danaher retention
Business Acquisition [Line Items]
Post combination compensation expense						$ 6,700,000		6,700,000
Common stock
Business Acquisition [Line Items]
Share price (in dollars per share)											$ 36.89
Avvasi
Business Acquisition [Line Items]
Estimated Purchase Price	$ 4,606,000
Contingent purchase consideration	660,000
Goodwill	$ 1,950,000
Weighted average useful life of acquired intangible assets	10 years 10 months 24 days
Avvasi | Service Assurance
Business Acquisition [Line Items]
Goodwill	$ 2,000,000
Communications Business
Business Acquisition [Line Items]
Estimated Purchase Price		$ 5,700,000	$ 2,270,556,000
Goodwill		5,141,000	1,510,665,000		$ 5,141,000					1,500,000,000
Weighted average useful life of acquired intangible assets							14 years 8 months
Total equity consideration		$ 5,700,000	$ 2,299,911,000		$ 2,300,000,000
Decrease in prepaid expenses and other current assets							$ 200,000
Increase in deferred income taxes							700,000
Increase in deferred tax liabilities							3,300,000
Increase in goodwill							2,800,000
Revenues							344,700,000
Net loss							10,300,000
Communications Business | General and administrative
Business Acquisition [Line Items]
Acquisition related costs							$ 0	$ 17,900,000
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 | Service Assurance
Business Acquisition [Line Items]
Goodwill										976,500,000
Communications Business | Security
Business Acquisition [Line Items]
Goodwill										$ 534,800,000
Communications Business | Common stock | Newco
Business Acquisition [Line Items]
Shares issued in business acquisition (in shares)			62.5
Forecast | Avvasi
Business Acquisition [Line Items]
Contingent purchase consideration									$ 660,000