ACQUISITIONS - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions				12 Months Ended
	Jul. 12, 2017	Aug. 19, 2016	Jul. 14, 2015	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Jul. 13, 2015
Business Acquisition [Line Items]
Fair value of contingent liability				$ 5,464,000	$ 5,449,000
Goodwill				$ 1,712,764,000	1,718,162,000	$ 1,709,369,000
Weighted average useful life of acquired intangible assets				14 years 7 months 2 days
Service Assurance reporting unit
Business Acquisition [Line Items]
Goodwill				$ 1,200,000,000	1,200,000,000
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]
Total equity consideration				$ 15,000,000
Percent of cancelled Danaher equity awards replaced				50.00%
Post combination compensation expense, Danaher equity awards | Vesting July 14, 2015 through August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense				$ 0	0	6,500,000
Post combination compensation expense, Danaher equity awards | Vesting after August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense				0	4,300,000	8,000,000
Post combination compensation expense, Danaher bonus
Business Acquisition [Line Items]
Post combination compensation expense				0	0	9,300,000
Post combination compensation expense, Danaher retention
Business Acquisition [Line Items]
Post combination compensation expense				0	0	$ 7,800,000
Common stock Voting
Business Acquisition [Line Items]
Share price (in dollars per share)							$ 36.89
Efflux Systems, Inc.
Business Acquisition [Line Items]
Estimated purchase price	$ 8,627,000
Fair value of contingent liability	523,000			$ 523,000
Goodwill	$ 6,077,000
Weighted average useful life of acquired intangible assets	10 years
Avvasi
Business Acquisition [Line Items]
Estimated purchase price		$ 4,600,000
Fair value of contingent liability					$ 660,000
Avvasi | Service Assurance reporting unit
Business Acquisition [Line Items]
Goodwill		$ 2,000,000
Communications Business
Business Acquisition [Line Items]
Total equity consideration			$ 2,300,000,000
Communications Business | Common stock Voting | Newco
Business Acquisition [Line Items]
Shares issued in business acquisition (in shares)			62.5