INCOME TAXES - Reconciliation of the Difference between the Actual Provisions for Income Taxes (Details)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	0.90%	2.70%	1.60%
Valuation allowances for deferred tax assets, including state	(3.70%)	(4.40%)	(1.30%)
Research and development credits	0.30%	0.70%	(1.30%)
Capitalized transaction costs	0.00%	0.00%	0.60%
Stock based compensation	(0.80%)	(0.10%)	(0.70%)
Goodwill Impairment	(12.30%)	(19.60%)	0.00%
Foreign income taxed at lower rates	0.00%	2.40%	(1.60%)
Reserves for uncertain tax positions	2.30%	0.30%	0.00%
Repatriation of foreign undistributed earnings	0.00%	0.00%	1.60%
CARES Act carryback benefit	1.40%	0.00%	0.00%
Pension plan settlement	0.00%	5.90%	0.00%
Other	(0.60%)	(0.60%)	(0.40%)
Effective income tax rate	8.50%	8.30%	19.50%

Effective Income Tax Rate Reconciliation, Carryback Benefit, Percent, CARES Act

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Effective Income Tax Rate Reconciliation, Nondeductible Expense, Capitalized Transaction Costs

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Effective Income Tax Rate Reconciliation, Nondeductible Expense, Litigation Settlement, Percent

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Effective Income Tax Rate Reconciliation, Reserves for Uncertain Tax Positions, Percent

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Topic 740
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

+ References

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for share-based payment arrangement.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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