REVENUE AND MAJOR CUSTOMERS (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($) Customer	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) Customer	Dec. 31, 2017 USD ($) Customer	Mar. 31, 2018 Customer
Revenue from External Customer [Line Items]
Revenue, Remaining Performance Obligation, Current	$ 138,700		$ 138,700
Net revenues	501,669,000	$ 226,534,000	$ 1,206,047,000	$ 640,760,000
Revenue From Contracts With Customers, Percentage Associated With Non-cancellable Maintenance And Support Contracts			90.00%
Contract with Customer, Liability	179,000,000		$ 179,000,000
Capitalized Contract Cost, Gross	1,900,000		1,900,000
Revenue, Remaining Performance Obligation, Noncurrent	55,400		55,400
Revenue, Remaining Performance Obligation, Amount	194,100		194,100
US [Member]
Revenue from External Customer [Line Items]
Net revenues	223,111,000	106,455,000	570,726,000	326,360,000
Europe and Africa [Member]
Revenue from External Customer [Line Items]
Net revenues	146,388,000	73,620,000	338,935,000	184,761,000
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Net revenues	90,162,000	27,553,000	204,504,000	75,664,000
Americas, excluding U.S. [Member]
Revenue from External Customer [Line Items]
Net revenues	42,008,000	18,906,000	91,882,000	53,975,000
Total international net revenues [Member]
Revenue from External Customer [Line Items]
Net revenues	278,558,000	120,079,000	635,321,000	314,400,000
Enterprise Headset [Member]
Revenue from External Customer [Line Items]
Net revenues	173,479,000	167,640,000	511,099,000	485,152,000
Consumer Headset [Member]
Revenue from External Customer [Line Items]
Net revenues	69,665,000	58,894,000	181,385,000	155,608,000
Voice [Member]
Revenue from External Customer [Line Items]
Net revenues	116,700,000	0	238,009,000	0
Video [Member]
Revenue from External Customer [Line Items]
Net revenues	85,597,000	0	171,519,000	0
Service [Member]
Revenue from External Customer [Line Items]
Net revenues	$ 56,228,000	$ 0	$ 104,035,000	$ 0
Net Revenues [Member] | Customer Concentration Risk [Member] | Ingram Micro [Member]
Revenue from External Customer [Line Items]
Number of major customers, ten percent or greater, net revenues | Customer				1
Concentration risk percentage	11.50%	10.70%	10.90%	11.60%
Net Revenues [Member] | Customer Concentration Risk [Member] | Ingram Micro And ScanSource [Member]
Revenue from External Customer [Line Items]
Number of major customers, ten percent or greater, net revenues | Customer			2
Net Revenues [Member] | Customer Concentration Risk [Member] | ScanSource [Member]
Revenue from External Customer [Line Items]
Concentration risk percentage	16.40%		15.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Ingram Micro [Member]
Revenue from External Customer [Line Items]
Concentration risk percentage			19.00%		12.40%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | D&H Distributors And Ingram Micro [Member]
Revenue from External Customer [Line Items]
Number of major customers, ten percent or greater, net accounts receivable | Customer					2
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Ingram Micro And ScanSource [Member]
Revenue from External Customer [Line Items]
Number of major customers, ten percent or greater, net accounts receivable | Customer	2		2
Accounts Receivable [Member] | Customer Concentration Risk [Member] | D&H Distributors [Member]
Revenue from External Customer [Line Items]
Concentration risk percentage					13.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | ScanSource [Member]
Revenue from External Customer [Line Items]
Concentration risk percentage			15.00%
Minimum [Member]
Revenue from External Customer [Line Items]
Revenue From Contracts With Customers, Credit Term			30 days
Maximum [Member]
Revenue from External Customer [Line Items]
Revenue From Contracts With Customers, Credit Term			90 days