ACQUISITIONS & DIVESTITURES - Narrative (Details) - USD ($)			1 Months Ended	12 Months Ended
	Sep. 14, 2018	Jul. 12, 2017	Sep. 30, 2018	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Business Acquisition [Line Items]
Loss on divestiture of business				$ 9,472,000	$ 0	$ 0
Goodwill				1,715,485,000	$ 1,712,764,000	$ 1,718,162,000
Efflux Systems, Inc.
Business Acquisition [Line Items]
Estimated purchase price		$ 8,600,000
Goodwill		$ 6,100,000
Handheld Network Test Tools Business | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Business Acquisition [Line Items]
Cash proceeds from divestiture	$ 1,300,000
Contingent consideration related to the divestiture	$ 2,300,000			800,000
Contingent consideration measurement period	2 years		2 years
Net liabilities transferred				4,600,000
Loss on divestiture of business				9,500,000
Transaction costs				1,300,000
Incentive compensation payable				500,000
Transitional services agreement	18 months
Transitional services within other expense				2,200,000
Change in fair value contingent consideration in other expense				1,600,000
Change in fair value contingent consideration in other assets				$ 800,000
Handheld Network Test Tools Business | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Maximum
Business Acquisition [Line Items]
Contingent consideration related to the divestiture	$ 4,000,000.0		$ 4,000,000.0