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INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Jun. 24, 2018 | Jan. 01, 2018
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Tax credit carryforward | $ 32,900 |  |  |  |
Significant change in shareholder ownership, period of change | 3 years |  |  |  |
Significant change in shareholder ownership, benchmark percentage | 50.00% |  |  |  |
Decrease in deferred tax assets | $ (4,959) | $ (9,152) |  |  |
BEAT tax expense |  |  | $ 400 |  |
Decrease in valuation allowance | 500 | 200 |  |  |
Deferred tax assets, valuation allowance | 94,980 | 101,484 |  |  |
Potential penalties and interest | 100 | 100 | 200 |  |
Interest and penalties accrued in deferred tax liability | 700 | 600 | 600 |  |
Income tax benefit | (7,182) | (3,400) | 18,440 |  |
Internal Revenue Service (IRS) |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Operating loss carryforwards | 224,800 |  |  |  |
Domestic Tax Authority |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Deferred tax assets, valuation allowance | 71,400 | 82,400 |  |  |
Edgewater |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Net operating loss carryforwards acquired |  |  |  | $ 34,000 |
Tax credit carryforwards acquired |  |  |  | $ 6,000 |
Deferred tax assets, valuation allowance | 200 |  |  |  |
Income tax benefit |  | 700 |  |  |
GENBAND |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Deferred tax assets, valuation allowance | 11,000 |  |  |  |
Income tax benefit |  |  | $ 16,400 |  |
IRELAND | GENBAND |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Deferred tax assets, valuation allowance | 9,200 | $ 9,500 |  |  |
BRAZIL | GENBAND |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Deferred tax assets, valuation allowance | $ 2,700 |  |  |  |
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Decrease in deferred tax assets |  |  |  |  | $ 2,200

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