FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of financial instruments measured at fair value on recurring basis

Financial instruments measured at fair value on a recurring basis as of March 31, 2018 and December 31, 2017 are classified based on the valuation technique in the table below:

	March 31, 2018
	Fair value measurements using
(in thousands)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
U.S. Treasury securities	$	—	$	19,842	$	—	$	19,842
Money market accounts	56,273		—		—		56,273
Total assets at fair value	$	56,273	$	19,842	$	—	$	76,115

	December 31, 2017
	Fair value measurements using
(in thousands)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
U.S. Treasury securities	$	—	$	21,916	$	—	$	21,916
Money market accounts	1,117		—		—		1,117
Total assets at fair value	$	1,117	$	21,916	$	—	$	23,033

Schedule of short-term investments

Short-term Investments

	March 31, 2018
(in thousands)	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. Treasury securities	$	19,860	$	—	$	(18	)	$	19,842
Total	$	19,860	$	—	$	(18	)	$	19,842

	December 31, 2017
(in thousands)	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. Treasury securities	$	21,939	$	—	$	(23	)	$	21,916
Total	$	21,939	$	—	$	(23	)	$	21,916