CASH EQUIVALENTS AND INVESTMENTS - Schedule of Cash Equivalents and Investments by Measurement (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	$ 310	$ 1,254
Marketable securities, fair value	7,284	17,224
Investments, fair value	0	9,031
Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	310	1,254
Marketable securities, fair value	0	0
Investments, fair value		0
Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	0	0
Marketable securities, fair value	7,284	17,224
Investments, fair value		9,031
Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Cash equivalents, fair value	0	0
Marketable securities, fair value	0	0
Investments, fair value		0
U.S. government agency notes
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,989	4,072
Investments, fair value		3,964
U.S. government agency notes \| Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
U.S. government agency notes \| Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,989	4,072
Investments, fair value		3,964
U.S. government agency notes \| Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
Corporate debt securities
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,295	8,017
Investments, fair value		3,884
Corporate debt securities \| Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	0	0
Investments, fair value		0
Corporate debt securities \| Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	3,295	8,017
Investments, fair value		3,884
Corporate debt securities \| Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value	$ 0	0
Investments, fair value		0
Certificates of deposit
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		5,135
Investments, fair value		1,183
Certificates of deposit \| Quoted prices in active markets (Level 1)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		0
Investments, fair value		0
Certificates of deposit \| Significant other observable inputs (Level 2)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		5,135
Investments, fair value		1,183
Certificates of deposit \| Significant unobservable inputs (Level 3)
Cash and cash equivalents, Marketable securities and Investments
Marketable securities, fair value		0
Investments, fair value		$ 0

Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
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