MAJOR CUSTOMERS, PARTNERSHIPS AND STRATEGIC ALLIANCES - Pfizer Inc. (Detail)	1 Months Ended			3 Months Ended		12 Months Ended	52 Months Ended	59 Months Ended
	Sep. 30, 2020 USD ($)	Dec. 31, 2017 USD ($)	May 31, 2017 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2022 USD ($) milestone royalty_fee	Mar. 31, 2022 USD ($) milestone product
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues				$ 28,231,000	$ 26,280,000
Pfizer Inc.
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Agreement termination, term			15 years
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. | Other products
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone revenue receivable			175,000,000
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 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	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 | royalty_fee							0
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
Pfizer C9ORF72 | C9ORF72
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement		12,000,000
Revenues				$ 0	$ 0
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