REVENUE AND MAJOR CUSTOMERS (Details)	3 Months Ended								12 Months Ended
	Mar. 31, 2019 USD ($) Customer	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($) Customer	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2019 USD ($) Customer	Mar. 31, 2018 USD ($) Customer	Mar. 31, 2017 USD ($) Customer
Revenue from External Customer [Line Items]
Revenue, Remaining Performance Obligation, Current	$ 142,100								$ 142,100
Net revenues	468,488,000	$ 501,669,000	$ 483,069,000	$ 221,309,000	$ 216,143,000	$ 226,534,000	$ 210,300,000	$ 203,926,000	1,674,535,000	$ 856,903,000	$ 881,176,000
Contract with Customer, Liability	193,900,000				$ 3,000,000				$ 193,900,000	$ 3,000,000	$ 2,000,000
Contract with Customer, Liability, Percentage Of Revenue									11.60%	1.00%
Number of major customers, ten percent or greater, net accounts receivable | Customer											1
Capitalized Contract Cost, Gross	3,100,000								$ 3,100,000
Revenue, Remaining Performance Obligation, Noncurrent	60,700								60,700
Revenue, Remaining Performance Obligation, Amount	$ 202,800								202,800
U.S.
Revenue from External Customer [Line Items]
Net revenues									789,545,000	$ 434,053,000	$ 482,215,000
Europe and Africa [Member]
Revenue from External Customer [Line Items]
Net revenues									476,891,000	250,763,000	226,620,000
Asia Pacific
Revenue from External Customer [Line Items]
Net revenues									288,880,000	99,779,000	106,295,000
Americas, excluding U.S.
Revenue from External Customer [Line Items]
Net revenues									119,219,000	72,308,000	66,046,000
Total international net revenues [Member]
Revenue from External Customer [Line Items]
Net revenues									884,990,000	422,850,000	398,961,000
Enterprise Headset [Member]
Revenue from External Customer [Line Items]
Net revenues									680,881,000	649,739,000	628,654,000
Consumer Headset [Member]
Revenue from External Customer [Line Items]
Net revenues									229,817,000	207,164,000	252,522,000
Voice [Member]
Revenue from External Customer [Line Items]
Net revenues									344,586,000	0	0
Video [Member]
Revenue from External Customer [Line Items]
Net revenues									255,485,000	0	0
Service [Member]
Revenue from External Customer [Line Items]
Net revenues									$ 163,765,000	$ 0	$ 0
Net Revenues [Member] | Customer concentration risk | Ingram Micro [Member]
Revenue from External Customer [Line Items]
Number of major customers, ten percent or greater, net revenues | Customer										1
Concentration risk percentage									11.40%	10.90%
Net Revenues [Member] | Customer concentration risk | ScanSource [Member]
Revenue from External Customer [Line Items]
Concentration risk percentage									16.00%
Accounts receivable | Customer concentration risk | Ingram Micro [Member]
Revenue from External Customer [Line Items]
Concentration risk percentage									21.30%	12.40%
Accounts receivable | Customer concentration risk | Scansource, 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	3								3
Accounts receivable | Customer concentration risk | 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					2
Accounts receivable | Customer concentration risk | D&H Distributors [Member]
Revenue from External Customer [Line Items]
Concentration risk percentage									10.90%	13.00%
Accounts receivable | Customer concentration risk | ScanSource [Member]
Revenue from External Customer [Line Items]
Concentration risk percentage									19.20%