REVENUE RECOGNITION - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 819,760	$ 844,957	$ 843,795
Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	508,137	556,656	583,270
IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	311,623	288,301	260,525
Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	442,680	453,042	467,912
Product revenue \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	215,770	248,570	275,445
Product revenue \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	226,910	204,472	192,467
Product revenue \| Sales to enterprise customers
Disaggregation of Revenue [Line Items]
Total revenue	125,664	111,494	138,469
Product revenue \| Sales to service provider customers
Disaggregation of Revenue [Line Items]
Total revenue	317,016	341,548	329,443
Product revenue \| Indirect sales through channel program
Disaggregation of Revenue [Line Items]
Total revenue	131,998	117,065	134,876
Product revenue \| Direct sales
Disaggregation of Revenue [Line Items]
Total revenue	310,682	335,977	333,036
Service
Disaggregation of Revenue [Line Items]
Total revenue	377,080	391,915	375,883
Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	282,095	286,321	274,816
Service revenue (maintenance) \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	222,238	228,321	229,035
Service revenue (maintenance) \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	59,857	58,000	45,781
Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	94,985	105,594	101,067
Service revenue (professional services) \| Cloud and Edge
Disaggregation of Revenue [Line Items]
Total revenue	70,130	79,765	78,790
Service revenue (professional services) \| IP Optical Networks
Disaggregation of Revenue [Line Items]
Total revenue	24,855	25,829	22,277
United States
Disaggregation of Revenue [Line Items]
Total revenue	352,663	376,037	382,619
United States \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	175,189	196,058	201,347
United States \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	132,655	132,683	132,661
United States \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	44,819	47,296	48,611
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	252,781	248,027	248,268
Europe, Middle East and Africa \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	147,523	138,203	149,567
Europe, Middle East and Africa \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	75,948	79,475	73,475
Europe, Middle East and Africa \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	29,310	30,349	25,226
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	151,099	152,931	146,456
Asia Pacific \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	95,828	92,803	90,201
Asia Pacific \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	41,677	41,945	36,628
Asia Pacific \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	13,594	18,183	19,627
Other
Disaggregation of Revenue [Line Items]
Total revenue	63,217	67,962	66,452
Other \| Product revenue
Disaggregation of Revenue [Line Items]
Total revenue	24,140	25,978	26,797
Other \| Service revenue (maintenance)
Disaggregation of Revenue [Line Items]
Total revenue	31,815	32,218	32,052
Other \| Service revenue (professional services)
Disaggregation of Revenue [Line Items]
Total revenue	$ 7,262	$ 9,766	$ 7,603