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INTANGIBLE ASSETS AND GOODWILL - Schedule of Changes in Carrying Value of Goodwill (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2021
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Goodwill [Roll Forward]        
Goodwill at the beginning of the period   $ 300,892,000 $ 416,892,000  
Impairment of goodwill   0 (116,000,000) $ 0
Goodwill, Ending Balance $ 300,892,000 300,892,000 300,892,000 416,892,000
Accumulated impairment losses (283,406,000) (283,406,000) (283,406,000)  
Cloud and Edge        
Goodwill [Roll Forward]        
Goodwill at the beginning of the period   224,896,000 224,896,000  
Impairment of goodwill 0      
Goodwill, Ending Balance 224,896,000 224,896,000 224,896,000 224,896,000
Accumulated impairment losses (167,406,000) (167,406,000) (167,406,000)  
IP Optical Networks        
Goodwill [Roll Forward]        
Goodwill at the beginning of the period   75,996,000 191,996,000  
Impairment of goodwill (116,000,000)      
Goodwill, Ending Balance 75,996,000 75,996,000 75,996,000 $ 191,996,000
Accumulated impairment losses $ (116,000,000) (116,000,000) (116,000,000)  
ECI        
Goodwill [Roll Forward]        
Impairment of goodwill   0 (116,000,000)  
Goodwill, Ending Balance   191,996,000    
ECI | Cloud and Edge        
Goodwill [Roll Forward]        
Impairment of goodwill   0 0  
ECI | IP Optical Networks        
Goodwill [Roll Forward]        
Impairment of goodwill   $ 0 $ (116,000,000)