FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018
	Total		Level 1		Level 2		Level 3
Assets
Cash and cash equivalents:
Cash	$	3,731	$	3,731	$	—	$	—
Money market funds	28,963		28,963		—		—
Total cash and cash equivalents	32,694		32,694		—		—
Short-term investments:
U.S. Treasury bills	3,771		3,771		—		—
Corporate debt securities	111,916		—		111,916		—
Commercial paper	74,409		—		74,409		—
Total short-term investments	190,096		3,771		186,325		—
Total	$	222,790	$	36,465	$	186,325	$	—

	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	$	—