FAIR VALUE MEASUREMENTS - Maturity of available-for-sale securities by contractual maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
FAIR VALUE MEASUREMENTS AND SHORT-TERM INVESTMENTS
Available For Sale Securities Debt Maturities After One Year or Less Amortized Cost	$ 18,796	$ 16,823
Available For Sale Securities Debt Maturities After One Year Through Five Years Amortized Cost	18,893	9,501
Available For Sale Securities Debt Maturities Within Five Years Amortized Cost		10,454
Available-for-sale Securities, Amortized Cost	37,689	36,778
Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	18,796	16,851
Available For Sale Securities Debt Maturities After One Through Five Years Fair Value	18,945	9,480
Available For Sale Securities Debt Maturities Within Five Years Fair Value		10,454
Debt Securities, Available-for-sale, Total	$ 37,741	$ 36,785

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amortized cost of investment in debt security measured at fair value with change recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), maturing in next fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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It represents the amount of available for sale securities debt maturities within five years amortized cost.

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Amount due in five years.

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