INCOME TAXES - Reconciliation of Expected Income Tax Expense (Details)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation:
United States federal statutory income tax rate	21.00%	21.00%	34.00%
Impact of foreign rate differential	4.40%	1.60%	(2.60%)
State taxes, net of federal benefit	0.60%	1.30%	1.40%
Stock option cancellations	0.00%	(1.20%)	(0.80%)
Contingent consideration	(18.00%)	(5.50%)	(10.70%)
General business credits and other credits	0.40%	0.70%	0.80%
Permanent differences	0.00%	(0.30%)	0.30%
Other	(0.50%)	0.50%	0.00%
United States federal statutory tax rate change	0.00%	0.00%	(50.60%)
Change in valuation allowance	(7.90%)	(18.10%)	28.20%
Effective Income Tax Rate	0.00%	0.00%	0.00%

Effective Income Tax Rate Reconciliation Contingent Consideration, Percent

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Effective Income Tax Rate Reconciliation Permanent Differences

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

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

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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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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.

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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 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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