FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value, Assets Measured on Recurring Basis

The following table summarizes the assets and liabilities measured at fair value on a recurring basis (in thousands):

	December 31, 2017
	Total		Level 1		Level 2		Level 3
Assets
Cash and cash equivalents:
Cash	$	1,026	$	1,026	$	—	$	—
Money market funds	106,677		106,677		—		—
Total cash and cash equivalents	107,703		107,703		—		—
Short-term investments:
Corporate debt securities	24,241		—		24,241		—
Commercial paper	18,893		—		18,893		—
Total short-term investments	43,134		—		43,134		—
Total	$	150,837	$	107,703	$	43,134	$	—

	December 31, 2016
	Total		Level 1		Level 2		Level 3
Assets
Cash and cash equivalents:
Cash	$	2,728	$	2,728	$	—	$	—
Money market funds	19,655		19,655		—		—
Total cash and cash equivalents	22,383		22,383		—		—
Short-term investments:
Corporate debt securities	20,619		—		20,619		—
Commercial paper	13,732		—		13,732		—
Total short-term investments	34,351		—		34,351		—
Total	$	56,734	$	22,383	$	34,351	$	—