FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Assets
Total marketable securities	$ 59,549	$ 93,001
Level 1
Fair Value Assets
Total marketable securities	0	0
Level 2
Fair Value Assets
Total marketable securities	59,549	93,001
Level 3
Fair Value Assets
Total marketable securities	0	0
Cash equivalents
Fair Value Assets
Cash equivalents	5,653	20,155
Cash equivalents \| Level 1
Fair Value Assets
Cash equivalents	5,653	10,155
Cash equivalents \| Level 2
Fair Value Assets
Cash equivalents	0	10,000
Cash equivalents \| Level 3
Fair Value Assets
Cash equivalents	0	0
Municipal bonds
Fair Value Assets
Total marketable securities	29,646	44,705
Municipal bonds \| Level 1
Fair Value Assets
Total marketable securities	0	0
Municipal bonds \| Level 2
Fair Value Assets
Total marketable securities	29,646	44,705
Municipal bonds \| Level 3
Fair Value Assets
Total marketable securities	0	0
Corporate bonds
Fair Value Assets
Total marketable securities	29,903	48,296
Corporate bonds \| Level 1
Fair Value Assets
Total marketable securities	0	0
Corporate bonds \| Level 2
Fair Value Assets
Total marketable securities	29,903	48,296
Corporate bonds \| Level 3
Fair Value Assets
Total marketable securities	0	0
Investments in privately-held companies
Fair Value Assets
Investments in privately-held companies	3,890	3,390
Investments in privately-held companies \| Level 1
Fair Value Assets
Investments in privately-held companies	0	0
Investments in privately-held companies \| Level 2
Fair Value Assets
Investments in privately-held companies	0	0
Investments in privately-held companies \| Level 3
Fair Value Assets
Investments in privately-held companies	$ 3,890	$ 3,390

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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.

+ References

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ 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 (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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