MAJOR CUSTOMERS, PARTNERSHIPS AND STRATEGIC ALLIANCES - Pfizer Inc. (Details)	1 Months Ended				3 Months Ended		12 Months Ended			13 Months Ended	49 Months Ended	56 Months Ended
	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)	May 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2021 USD ($) royaltyFee product	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) milestone	Dec. 31, 2021 USD ($) milestone
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues							$ 110,701,000	$ 118,192,000	$ 102,428,000
Pfizer SB-525
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement							55,000,000
Collaborative arrangement transaction price							134,000,000
Research service fees							79,000,000
Revenues							$ 0
Pfizer SB-525 | S B Five Two Five And Other Products
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaborative arrangement, number of milestones achieved | milestone												2
Milestone payments received												$ 55,000,000
Number of products approved | product							0
Number of milestones included in transaction price | royaltyFee							0
Pfizer, Giroctocogene Fitelparvovec
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement		$ 25,000,000
Revenues							$ 0	34,449,000	39,359,000
Collaborative arrangement, increase (decrease) in revenue								(2,400,000)
Collaborative arrangement, increase (decrease) in net income (loss)								$ 2,400,000
Collaborative arrangement, net income (loss) per share | $ / shares								$ 0.02
Pfizer, Giroctocogene Fitelparvovec | Phase Three Clinical Trial
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Development and sales-based milestone payments to be received	$ 30,000,000
Cumulative compensation earned								$ 30,000,000		$ 30,000,000
Pfizer, Giroctocogene Fitelparvovec | Amended collaboration and license agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Recognition of milestone								1,300,000		$ 25,000,000
Pfizer, Giroctocogene Fitelparvovec | Recognition of license and stand-ready fee
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues					$ 8,700,000		0	3,111,000	15,697,000
Reduction in revenues						$ 3,000,000
Pfizer, Giroctocogene Fitelparvovec | Milestone achievement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues							$ 0	31,338,000	23,662,000
Pfizer Inc.
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Agreement termination, term							15 years
Collaborative arrangement, increase (decrease) in revenue								(8,800,000)
Collaborative arrangement, increase (decrease) in net income (loss)								$ 8,800,000
Collaborative arrangement, net income (loss) per share | $ / shares								$ (0.06)
Pfizer Inc. | S B Five Two Five And Other Products
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement				$ 70,000,000
Potential amount to be funded for achievement of specified commercialized and sales milestones				266,500,000
Milestone revenue receivable				300,000,000
Pfizer Inc. | S B Five Two Five And Other Products | Achievement of specified clinical development intellectual property and regulatory milestones
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Development and sales-based milestone payments to be received				208,500,000
Pfizer Inc. | S B Five Two Five And Other Products | Achievement of first commercial sale milestones
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Development and sales-based milestone payments to be received				475,000,000
Pfizer Inc. | C9ORF72
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement			$ 5,000,000					$ 5,000,000
Development and sales-based milestone payments to be received	$ 5,000,000
Collaborative arrangement transaction price			17,000,000
Pfizer Inc. | Other products
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone revenue receivable				$ 175,000,000
Pfizer C9ORF72
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Agreement termination, term							15 years
Milestone payments received			12,000,000								$ 5,000,000
Number of products approved | milestone											0
Number of milestones included in transaction price | milestone											0
Revenues							$ 0	12,985,000	1,827,000
Pfizer C9ORF72 | Recognition of license and stand-ready fee
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues							0	7,985,000	1,827,000
Pfizer C9ORF72 | Milestone achievement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues							$ 0	$ 5,000,000	$ 0
Pfizer C9ORF72 | C9ORF72
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement			12,000,000
Pfizer C9ORF72 | C9ORF72 | Achievement of specified preclinical development clinical development and first commercial sale milestones | Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Development and sales-based milestone payments to be received			60,000,000
Pfizer C9ORF72 | C9ORF72 | Achievement of commercial milestones | Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Development and sales-based milestone payments to be received			$ 90,000,000