ACQUISITIONS - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions		3 Months Ended	6 Months Ended
	Jul. 14, 2015	Sep. 30, 2015	Sep. 30, 2015	Jul. 13, 2015	Mar. 31, 2015
Business Acquisition [Line Items]
Goodwill		$ 1,702,705	$ 1,702,705		$ 197,445
Weighted average useful life of acquired intangible assets			14 years 7 months
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
Arbor Networks
Business Acquisition [Line Items]
Goodwill		534,700	$ 534,700
Tektronix Communications
Business Acquisition [Line Items]
Goodwill		793,300	793,300
VSS
Business Acquisition [Line Items]
Goodwill		57,000	57,000
FNET
Business Acquisition [Line Items]
Goodwill		$ 119,700	$ 119,700
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%
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	$ 6,500
Post combination compensation expense, Danaher equity awards | Vesting after August 4, 2015
Business Acquisition [Line Items]
Post combination compensation expense		2,600	2,600
Contingently returnable consideration, cash retention award | Prepaid expenses and other current assets
Business Acquisition [Line Items]
Receivable from Danaher		5,000	5,000
Contingently returnable consideration, cash retention award | Vesting after August 4, 2015 | Prepaid expenses and other current assets
Business Acquisition [Line Items]
Receivable from Danaher		8,400	8,400
Cash retention award | Accrued compensation
Business Acquisition [Line Items]
Cash liability		6,700	6,700
Cash retention award | Vesting after August 4, 2015 | Accrued compensation
Business Acquisition [Line Items]
Cash liability		2,600	2,600
Contingently returnable consideration, cash incentive bonus | Prepaid expenses and other current assets
Business Acquisition [Line Items]
Receivable from Danaher		5,800	5,800
Cash incentive bonus | Accrued compensation
Business Acquisition [Line Items]
Cash liability		4,100	4,100
Post combination compensation expense, Danaher bonus
Business Acquisition [Line Items]
Post combination compensation expense		4,100	4,100
Post combination compensation expense, Danaher retention
Business Acquisition [Line Items]
Post combination compensation expense		$ 6,700	$ 6,700
Communications Business
Business Acquisition [Line Items]
Total equity consideration	$ 2,305,611
Goodwill	1,504,261
Weighted average useful life of acquired intangible assets			14 years 8 months
Revenues			$ 168,800
Net loss			19,500
Communications Business | General and administrative
Business Acquisition [Line Items]
Acquisition related costs			$ 17,900
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 | Trademarks and trade names
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible assets			8 years 6 months
Communications Business | Arbor Networks
Business Acquisition [Line Items]
Goodwill	534,700
Communications Business | Tektronix Communications
Business Acquisition [Line Items]
Goodwill	792,900
Communications Business | VSS
Business Acquisition [Line Items]
Goodwill	57,000
Communications Business | FNET
Business Acquisition [Line Items]
Goodwill	$ 119,700
Common stock
Business Acquisition [Line Items]
Share price (in dollars per share)				$ 36.89
Common stock | Newco | Communications Business
Business Acquisition [Line Items]
Shares issued in business acquisition (in shares)	62.5