FAIR VALUE MEASUREMENTS (Tables)

6 Months Ended

Jun. 30, 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 June 30, 2018 and December 31, 2017 are classified based on the valuation technique in the table below:

	June 30, 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	$	—	$	20,245	$	—	$	20,245
Money market accounts	86,583		—		—		86,583
Total assets at fair value	$	86,583	$	20,245	$	—	$	106,828

	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

	June 30, 2018
(in thousands)	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. Treasury securities	$	20,258	$	—	$	(13	)	$	20,245
Total	$	20,258	$	—	$	(13	)	$	20,245

	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