ACQUISITIONS - Avvasi and Communications Business (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			3 Months Ended		6 Months Ended
	Aug. 19, 2016	Jul. 14, 2015	Sep. 30, 2016	Oct. 07, 2015	Sep. 30, 2016	Sep. 30, 2017	Mar. 31, 2017	Jul. 13, 2015
Business Acquisition [Line Items]
Goodwill						$ 1,715,861	$ 1,718,162
Service Assurance
Business Acquisition [Line Items]
Goodwill						$ 1,200,000	$ 1,200,000
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]
Percent of cancelled Danaher equity awards replaced						50.00%
Business acquisition, equity interest issued, value						$ 15,000
Post combination compensation expense, Danaher equity awards | Vesting after August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense			$ 2,600		$ 4,300
Common stock
Business Acquisition [Line Items]
Share price (in dollars per share)								$ 36.89
Avvasi
Business Acquisition [Line Items]
Estimated purchase price	$ 4,600
Avvasi | Service Assurance
Business Acquisition [Line Items]
Goodwill	$ 2,000
Communications Business
Business Acquisition [Line Items]
Total equity consideration				$ 2,300,000
Communications Business | Common stock | Newco
Business Acquisition [Line Items]
Shares issued in business acquisition (in shares)		62.5