CASH, CASH EQUIVALENTS AND SHORT TERM INVESTMENTS - Summary of Securities Classifies as Cash and Cash Equivalents and Short-term Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 75,462	$ 110,949
Fair Value	75,462	110,949
Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,114
Commercial paper and Corporate and Government debt securities with maturities less than 1 year	7,114
Fair Value	7,114
Cash and cash equivalents
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	68,348
Fair Value	68,348
Cash \| Cash and cash equivalents
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	59,986	95,660
Fair Value	59,986	95,660
Commercial paper \| Cash and cash equivalents
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,239	14,028
Fair Value	8,239	14,028
Money market funds \| Cash and cash equivalents
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	123	11
Fair Value	$ 123	11
Agency bond \| Cash and cash equivalents
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,250
Fair Value		$ 1,250

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=82897076&loc=d3e27161-111563

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27198-111563

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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).

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

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