REVENUE RECOGNITION - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 231,118	$ 137,653	$ 599,593	$ 402,002
Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	128,926	61,152	325,687	180,691
Product revenue \| Sales to enterprise customers
Disaggregation of Revenue [Line Items]
Total revenue	36,937	17,458	100,168	47,295
Product revenue \| Sales to service provider customers
Disaggregation of Revenue [Line Items]
Total revenue	91,989	43,694	225,519	133,396
Product revenue \| Indirect sales through channel partner program
Disaggregation of Revenue [Line Items]
Total revenue	36,586	21,537	97,839	69,380
Product revenue \| Direct sales
Disaggregation of Revenue [Line Items]
Total revenue	92,340	39,615	227,848	111,311
Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	73,642	58,901	203,333	173,031
Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	28,550	17,600	70,573	48,280
United States
Disaggregation of Revenue [Line Items]
Total revenue	104,850	87,523	284,854	240,725
United States \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	57,503	44,701	150,980	114,525
United States \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	33,275	32,709	98,392	99,281
United States \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	14,072	10,113	35,482	26,919
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	68,118	20,880	167,393	71,930
Europe, Middle East and Africa \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	41,265	7,346	97,431	32,215
Europe, Middle East and Africa \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	19,720	10,899	54,042	31,016
Europe, Middle East and Africa \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	7,133	2,635	15,920	8,699
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	39,624	15,859	99,789	51,236
Asia Pacific \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	22,233	5,517	59,030	23,217
Asia Pacific \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	12,208	7,123	26,742	20,272
Asia Pacific \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	5,183	3,219	14,017	7,747
Other
Disaggregation of Revenue [Line Items]
Total revenue	18,526	13,391	47,557	38,111
Other \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	7,925	3,588	18,246	10,734
Other \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	8,439	8,170	24,157	22,462
Other \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,162	$ 1,633	$ 5,154	$ 4,915