SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred commission cost (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Deferred costs - current	$ 161	$ 152
Deferred costs - noncurrent	82	77
Accounting Standards Update 2014-09 [Member]
Deferred costs - current	161	152
Deferred costs - noncurrent	82	77
Total deferred costs	$ 243	$ 229