SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Financial Instruments Recognized at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Short-term available-for-sale investments		$ 415
Total current assets recorded at fair value		415
Restricted cash	$ 3,797	3,732
Total non-current assets recorded at fair value	3,797	3,732
Fair Value, Inputs, Level 1
Short-term available-for-sale investments		415
Total current assets recorded at fair value		415
Restricted cash	3,797	3,732
Total non-current assets recorded at fair value	3,797	3,732
Fair Value, Inputs, Level 2
Short-term available-for-sale investments
Total current assets recorded at fair value
Restricted cash
Total non-current assets recorded at fair value
Fair Value, Inputs, Level 3
Short-term available-for-sale investments
Total current assets recorded at fair value
Restricted cash
Total non-current assets recorded at fair value