SHARE BASED COMPENSATION - Summary of unvested stock option outstanding (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Shares ( in thousands)
Unvested option, outstanding at the beginning (in shares)	6,496	5,575
Unvested options granted (in shares)	208	4,359
Unvested options vested (in shares)	(2,740)	(2,333)
Unvested forfeited or expired (in shares)	(81)	(1,105)
Unvested cancelled (in shares)	(148)
Unvested option, outstanding at the end (in shares)	3,735	6,496
Weighted average fair value
Weighted average fair value, unvested options outstanding at the beginning (in dollars per share)	$ 0.30	$ 0.07
Weighted average fair value, unvested options granted (in dollars per share)	0.44	0.44
Weighted average fair value, unvested options vested (in dollars per share)	0.23	0.10
Weighted average fair value, unvested options forfeited or expired (in dollars per share)	0.37	0.07
Weighted average fair value, unvested options cancelled (in dollars per share)	0.44
Weighted average fair value, unvested options outstanding at the end (in dollars per share)	$ 0.36	$ 0.30