BUSINESS ACQUISITIONS - Summary of Preliminary Allocation of Purchase Consideration (Details) - USD ($) $ in Thousands		3 Months Ended
	Nov. 14, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Cash consideration:
Net cash consideration		$ 346,852	$ 0
Fair value of assets acquired and liabilities assumed:
Goodwill		414,389	$ 389,196	$ 224,896	$ 383,655
ECI
Cash consideration:
Repayment of ECI outstanding debt obligations	$ 183,300	183,266
Cash paid to selling shareholders	139,200	139,244
Payment to selling shareholders from sale of ECI real estate assets		33,400
Less cash and restricted cash acquired		(9,058)
Net cash consideration	322,500	346,852
Fair value of Ribbon stock issued	$ 108,600	108,550
Fair value of total consideration		455,402
Fair value of assets acquired and liabilities assumed:
Current assets, net of cash and restricted cash acquired		131,447
Property and equipment		55,207
Goodwill		189,493
Other noncurrent assets		56,204
Deferred revenue		(7,731)
Other current liabilities		(143,873)
Deferred revenue, net of current		(6,641)
Deferred tax liability		(13,308)
Other long-term liabilities		(59,296)
Fair value of assets acquired and liabilities assumed		455,402
ECI | In-process research and development
Fair value of assets acquired and liabilities assumed:
Intangible assets		31,000
ECI | Developed technology
Fair value of assets acquired and liabilities assumed:
Intangible assets		106,900
ECI | Customer relationships
Fair value of assets acquired and liabilities assumed:
Intangible assets		114,000
ECI | Trade names
Fair value of assets acquired and liabilities assumed:
Intangible assets		$ 2,000