SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - BASIS OF PRESENTATION (Details) - USD ($)		3 Months Ended						9 Months Ended
	Apr. 01, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Net loss		$ (41,051,000)	$ (28,117,000)	$ (30,098,000)	$ (26,697,000)	$ (29,574,000)	$ (27,824,000)	$ (99,266,000)	$ (84,095,000)
Cash flows from operations								(92,198,000)	$ (73,388,000)
Accumulated deficit		(1,371,007,000)						(1,371,007,000)		$ (1,271,741,000)
Cash, restricted cash, cash equivalents, and marketable securities.		$ 195,151,000						$ 195,151,000
2022 Underwritten Public Offering
Issuance of common stock in connection with public offering (in shares)	53,333,334
Net cash proceeds from public offering after deducting underwriting discount and other offering expenses	$ 69,916,000
2022 Underwritten Public Offering | 2022 Pre-Funded Warrant
Warrant to purchase common stock, shares	18,095,238
2022 Underwritten Public Offering | 2022 Stock Purchase Warrants
Warrant to purchase common stock, shares	35,714,286