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FAIR VALUE MEASUREMENTS (Details) - Fair Value Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Total assets at fair value	$ 66,011	$ 74,657
Money market funds
Assets:
Fair value of assets	6,038	11,556
U.S. Treasury reverse repurchase agreements
Assets:
Fair value of assets	46,000	48,000
Corporate debt
Assets:
Fair value of assets	13,973	15,101
LEVEL 1
Assets:
Total assets at fair value	6,038	11,556
LEVEL 1 | Money market funds
Assets:
Fair value of assets	6,038	11,556
LEVEL 1 | U.S. Treasury reverse repurchase agreements
Assets:
Fair value of assets	0	0
LEVEL 1 | Corporate debt
Assets:
Fair value of assets	0	0
LEVEL 2
Assets:
Total assets at fair value	59,973	63,101
LEVEL 2 | Money market funds
Assets:
Fair value of assets	0	0
LEVEL 2 | U.S. Treasury reverse repurchase agreements
Assets:
Fair value of assets	46,000	48,000
LEVEL 2 | Corporate debt
Assets:
Fair value of assets	13,973	15,101
LEVEL 3
Assets:
Total assets at fair value	0	0
LEVEL 3 | Money market funds
Assets:
Fair value of assets	0	0
LEVEL 3 | U.S. Treasury reverse repurchase agreements
Assets:
Fair value of assets	0	0
LEVEL 3 | Corporate debt
Assets:
Fair value of assets		$ 0

X

- 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

No definition available.

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