Nature of Business	9 Months Ended
Sep. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	1. Nature of Business REGENXBIO Inc. (the Company) is a clinical-stage biotechnology company seeking to improve lives through the curative potential of gene therapy. The Company's investigational gene therapies use adeno-associated virus (AAV) vectors from its proprietary gene delivery platform (NAV Technology Platform). The NAV® Technology Platform has consisted of exclusive rights to a large portfolio of proprietary AAV vectors. The Company has developed a broad pipeline of gene therapy product candidates using the NAV Technology Platform as a one-time treatment to address an array of diseases. The Company was formed in 2008 in the State of Delaware and is headquartered in Rockville, Maryland. The Company's lead product candidates include ABBV-RGX-314 (surabgene lomparvovec, sura-vec) for the treatment of wet age-related macular degeneration (wet AMD) and diabetic retinopathy (DR), which is being developed and commercialized in collaboration with AbbVie Global Enterprises Ltd. (AbbVie), a subsidiary of AbbVie Inc., and RGX-202 for the treatment of Duchenne muscular dystrophy. Additional clinical-stage candidates include RGX-121 (clemidsogene lanparvovec) for the treatment of Mucopolysaccharidosis Type II (MPS II) and RGX-111 for the treatment of Mucopolysaccharidosis Type I (MPS I), which are being developed and commercialized in collaboration with Nippon Shinyaku Co., Ltd. (Nippon Shinyaku). In addition to its internal product development efforts, the Company has also selectively licensed the NAV Technology Platform and other intellectual property rights to other leading biotechnology and pharmaceutical companies (NAV Technology Licensees). As of September 30, 2026, the NAV Technology Platform was being applied by NAV Technology Licensees in two commercial products, Zolgensma® and Itvisma®, and in the preclinical and clinical development of various other licensed products. Additionally, the Company has licensed intellectual property rights to collaborators for the joint development and commercialization of certain product candidates. Liquidity The Company has incurred cumulative losses since inception and as of September 30, 2026, had generated an accumulated deficit of $1.23 billion. The Company's ability to transition to recurring profitability is dependent upon achieving a level of revenues adequate to support its cost structure, which depends heavily on the successful development, approval and commercialization of its product candidates. The Company may never achieve recurring profitability, and unless and until it does, will continue to need to raise additional capital through equity offerings, licensing and collaboration arrangements, or other non-dilutive financings. There is no assurance that the Company will be able to raise sufficient capital or obtain financing on favorable terms, or at all. As of September 30, 2026, the Company had cash, cash equivalents and marketable securities of $251.0 million. In October 2026, the Company received a payment of $39.0 million pursuant to a settlement agreement with Sarepta Therapeutics, Inc. (Sarepta). Please refer to Note 8 for further information regarding the settlement agreement with Sarepta. Management believes the Company's cash, cash equivalents and marketable securities as of September 30, 2026, along with the settlement proceeds received in October 2026, are sufficient to fund operations into the late fourth quarter of 2027. This estimate is based on the Company's current operating plan and excludes the potential effects of any future financings or material milestone payments that may be received under the Company's licensing and collaboration arrangements. The Company has based this estimate on assumptions that may prove to be wrong, and it could exhaust its capital resources sooner than expected. These conditions raise substantial doubt about the Company's ability to continue as a going concern within 12 months from the date these consolidated financial statements were issued. The Company’s ability to continue as a going concern will depend heavily on the successful development, approval and commercialization of its product candidates and its ability to raise additional capital to fund its operations. If the Company is unable to raise capital sufficient to meet its working capital needs in the future, it may be forced to delay expenditures, reduce the scope of its development activities or make other changes to its operating plans.

Nature of Business

9 Months Ended

Sep. 30, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

1. Nature of Business

REGENXBIO Inc. (the Company) is a clinical-stage biotechnology company seeking to improve lives through the curative potential of gene therapy. The Company's investigational gene therapies use adeno-associated virus (AAV) vectors from its proprietary gene delivery platform (NAV Technology Platform). The NAV® Technology Platform has consisted of exclusive rights to a large portfolio of proprietary AAV vectors. The Company has developed a broad pipeline of gene therapy product candidates using the NAV Technology Platform as a one-time treatment to address an array of diseases. The Company was formed in 2008 in the State of Delaware and is headquartered in Rockville, Maryland.

The Company's lead product candidates include ABBV-RGX-314 (surabgene lomparvovec, sura-vec) for the treatment of wet age-related macular degeneration (wet AMD) and diabetic retinopathy (DR), which is being developed and commercialized in collaboration with AbbVie Global Enterprises Ltd. (AbbVie), a subsidiary of AbbVie Inc., and RGX-202 for the treatment of Duchenne muscular dystrophy. Additional clinical-stage candidates include RGX-121 (clemidsogene lanparvovec) for the treatment of Mucopolysaccharidosis Type II (MPS II) and RGX-111 for the treatment of Mucopolysaccharidosis Type I (MPS I), which are being developed and commercialized in collaboration with Nippon Shinyaku Co., Ltd. (Nippon Shinyaku).

In addition to its internal product development efforts, the Company has also selectively licensed the NAV Technology Platform and other intellectual property rights to other leading biotechnology and pharmaceutical companies (NAV Technology Licensees). As of September 30, 2026, the NAV Technology Platform was being applied by NAV Technology Licensees in two commercial products, Zolgensma® and Itvisma®, and in the preclinical and clinical development of various other licensed products. Additionally, the Company has licensed intellectual property rights to collaborators for the joint development and commercialization of certain product candidates.

Liquidity

The Company has incurred cumulative losses since inception and as of September 30, 2026, had generated an accumulated deficit of $1.23 billion. The Company's ability to transition to recurring profitability is dependent upon achieving a level of revenues adequate to support its cost structure, which depends heavily on the successful development, approval and commercialization of its product candidates. The Company may never achieve recurring profitability, and unless and until it does, will continue to need to raise additional capital through equity offerings, licensing and collaboration arrangements, or other non-dilutive financings. There is no assurance that the Company will be able to raise sufficient capital or obtain financing on favorable terms, or at all.

As of September 30, 2026, the Company had cash, cash equivalents and marketable securities of $251.0 million. In October 2026, the Company received a payment of $39.0 million pursuant to a settlement agreement with Sarepta Therapeutics, Inc. (Sarepta). Please refer to Note 8 for further information regarding the settlement agreement with Sarepta. Management believes the Company's cash, cash equivalents and marketable securities as of September 30, 2026, along with the settlement proceeds received in October 2026, are sufficient to fund operations into the late fourth quarter of 2027. This estimate is based on the Company's current operating plan and excludes the potential effects of any future financings or material milestone payments that may be received under the Company's licensing and collaboration arrangements. The Company has based this estimate on assumptions that may prove to be wrong, and it could exhaust its capital resources sooner than expected. These conditions raise substantial doubt about the Company's ability to continue as a going concern within 12 months from the date these consolidated financial statements were issued. The Company’s ability to continue as a going concern will depend heavily on the successful development, approval and commercialization of its product candidates and its ability to raise additional capital to fund its operations. If the Company is unable to raise capital sufficient to meet its working capital needs in the future, it may be forced to delay expenditures, reduce the scope of its development activities or make other changes to its operating plans.