SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred Revenue, by Arrangement (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Deferred revenue - current	$ 7,500	$ 7,068
Deferred revenue - noncurrent	10	5
Total deferred revenue	$ 7,510	$ 7,073