FAIR VALUE MEASUREMENTS - SCHEDULE OF SHORT-TERM INVESTMENTS (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Short-term investments, amortized cost	$ 20,258	$ 21,939
Short-term investments, gross unrealized holding gains	0	0
Short-term investments, gross unrealized holding losses	(13)	(23)
Short-term investments, fair value	20,245	21,916
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Short-term investments, amortized cost	20,258	21,939
Short-term investments, gross unrealized holding gains	0	0
Short-term investments, gross unrealized holding losses	(13)	(23)
Short-term investments, fair value	$ 20,245	$ 21,916