FAIR VALUE MEASUREMENTS - Recurring (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Short-term Investments [Member]
Assets
Assets at fair value	$ 21,313	$ 38,477
Money Market Funds
Assets
Assets at fair value	8,636	12,146
Corporate Bonds
Assets
Assets at fair value	12,677	26,331
Warrant
Assets
Assets at fair value	$ 239	$ 673
Warrant \| Volatility
Assets
Equity Securities, FV-NI, Measurement Input	137	83
Input increase (decrease) assumption, as a percent	20.00%	20.00%
Estimated change in fair value due to change in input	$ 115	$ 260
Convertible note receivable
Assets
Assets at fair value	5,173	4,865
Notes Receivable [Member]
Assets
Assets at fair value	5,876	5,589
Fair Value, Inputs, Level 1 \| Short-term Investments [Member]
Assets
Assets at fair value	8,636	12,146
Fair Value, Inputs, Level 1 \| Money Market Funds
Assets
Assets at fair value	8,636	12,146
Fair Value, Inputs, Level 1 \| Corporate Bonds
Assets
Assets at fair value	0
Fair Value, Inputs, Level 2 \| Short-term Investments [Member]
Assets
Assets at fair value	12,677	26,331
Fair Value, Inputs, Level 2 \| Money Market Funds
Assets
Assets at fair value	0
Fair Value, Inputs, Level 2 \| Corporate Bonds
Assets
Assets at fair value	12,677	26,331
Fair Value, Inputs, Level 3 \| Short-term Investments [Member]
Assets
Assets at fair value	0
Fair Value, Inputs, Level 3 \| Money Market Funds
Assets
Assets at fair value	0
Fair Value, Inputs, Level 3 \| Corporate Bonds
Assets
Assets at fair value	0
Fair Value, Inputs, Level 3 \| Warrant
Assets
Assets at fair value	239	673
Fair Value, Inputs, Level 3 \| Convertible note receivable
Assets
Assets at fair value	5,173	4,865
Fair Value, Inputs, Level 3 \| Notes Receivable [Member]
Assets
Assets at fair value	$ 5,876	$ 5,589

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Value of input used to measure investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

The estimated amount of change in the fair value of the equity securities resulting from the assumed percentage change in the measurement input.

+ References

No definition available.

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+ References

No definition available.

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