SUMMARY OF SIGNIFICANT ACCOUNTING PRACTICES - Loss per share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive securities excluded from calculation of net loss per share	16,655,260	16,331,016	13,195,747
Stock option
Antidilutive securities excluded from calculation of net loss per share	12,520,865	12,615,638	9,494,712
Employee Stock Purchase Plan
Antidilutive securities excluded from calculation of net loss per share	85,227	37,259
Restricted stock units
Antidilutive securities excluded from calculation of net loss per share	1,110,010		22,916
Series A Convertible Preferred Stock
Antidilutive securities excluded from calculation of net loss per share	97,000	97,000	97,000
Series B Convertible Preferred Stock
Antidilutive securities excluded from calculation of net loss per share	2,842,158	3,581,119	3,581,119