MAJOR CUSTOMERS, PARTNERSHIPS AND STRATEGIC ALLIANCES - Sanofi S.A. (Narrative) (Details)		1 Months Ended	12 Months Ended			102 Months Ended	120 Months Ended
	Sep. 06, 2022 USD ($)	Jan. 31, 2014 USD ($) program	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) $ / shares	Jun. 28, 2022 USD ($)	Dec. 31, 2023 USD ($) product milestone
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues			$ 176,232,000	$ 111,299,000	$ 110,701,000
Accounts receivable			923,000	3,678,000			$ 923,000
Decrease in research and development expense			2,100,000
Prepaid Expenses and Other Current Assets
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Decrease in research and development expense			500,000
Sanofi S.A.
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of research programs | program		2
Revenues under agreement		$ 20,000,000
Revenues			0	3,260,000	3,114,000	$ 13,500,000
Number of products approved | product							0
Expenses reimbursable through December 31, 2023 (up to)	$ 7,000,000
Expenses reimbursable after December 31, 2023 (up to)	$ 5,300,000
Sanofi S.A. | Collaboration and License Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement						20,000,000
Number of milestones included in transaction price | milestone							0
Collaborative arrangement transaction price						96,300,000
Collaborative arrangement estimated reimbursable service costs						62,800,000
Accounts receivable			0	600,000			$ 0
Deferred revenue			$ 0	$ 1,100,000			$ 0
Sanofi S.A. | Collaboration and License Agreement | Milestone Three
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone revenue receivable						$ 13,500,000
Sanofi S.A. | Collaborative Arrangement | Change in Agreement Estimate, September 2021
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Increase (decrease) in revenue					1,600,000
Increase (decrease) in net loss					$ 1,600,000
Increase (decrease) in diluted net loss per share | $ / shares					$ 0.01
Increase (decrease) in basic net loss per share | $ / shares					$ 0.01