STOCK INCENTIVE PLANS - 2009 and 2019 Stock Option Plan (Details) - shares	1 Months Ended
	Apr. 30, 2019	Jan. 31, 2018	Nov. 09, 2021	Sep. 30, 2021	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized (in shares)	25,204,250
The 2009 Option Plan
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized (in shares)		17,030,280			16,495,150
Additional shares authorized (in shares)		535,130
The 2019 Option Plan
Share-based Compensation Arrangement by Share-based Payment Award
Additional shares authorized (in shares)	8,173,970
The 2019 Option Plan | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized (in shares)			16,856,770
The 2019 Option Plan | Common Stock, LT50
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized (in shares)			16,856,770
The 2019 Option Plan | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized (in shares)				8,679,380
The 2019 Option Plan | Restricted stock units | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized (in shares)				4,339,690
The 2019 Option Plan | Restricted stock units | Common Stock, LT50
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized (in shares)				4,339,690