ACQUISITIONS - Avvasi and Communications Business (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			3 Months Ended	9 Months Ended
	Aug. 19, 2016	Jul. 14, 2015	Oct. 07, 2015	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017	Jul. 13, 2015
Business Acquisition [Line Items]
Goodwill				$ 1,716,371		$ 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				$ 0	$ 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