Royalty Monetization Liabilities - Schedule of Changes in Royalty Monetization Liability (Detail) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2026	Dec. 31, 2025
Royalty Monetization Liabilities [Line Items]
Beginning balance	$ 187,017
Ending balance	185,678
Current portion	(12,114)	$ (39,609)
Non-current portion	173,564	$ 147,408
2020 Royalty Purchase Agreement
Royalty Monetization Liabilities [Line Items]
Beginning balance	29,672
Ending balance	9,416
2020 Royalty Purchase Agreement \| HCR [Member]
Royalty Monetization Liabilities [Line Items]
Beginning balance	29,672
Novartis royalties paid to HCR	(25,246)
Interest expense recognized	4,990
Ending balance	9,416
Current portion	(9,416)
Non-current portion	0
2025 Royalty Bond
Royalty Monetization Liabilities [Line Items]
Beginning balance	157,345
Ending balance	176,262
2025 Royalty Bond \| HCR [Member]
Royalty Monetization Liabilities [Line Items]
Beginning balance	157,345
Unpaid interest accrued to principal	17,770
Amortization of debt discount and issuance costs	1,147
Ending balance	176,262
Current portion	(2,698)
Non-current portion	$ 173,564

Liability related to interest expense recognized.

No definition available.

Name:	rgnx_LiabilityRelatedToInterestExpenseRecognized
Namespace Prefix:	rgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Royalty monetization liabilities.

+ References

No definition available.

+ Details

Name:	rgnx_RoyaltyMonetizationLiabilities
Namespace Prefix:	rgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Royalty monetization liabilities current.

+ References

No definition available.

+ Details

Name:	rgnx_RoyaltyMonetizationLiabilitiesCurrent
Namespace Prefix:	rgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Royalty monetization liabilities.

+ References

No definition available.

+ Details

Name:	rgnx_RoyaltyMonetizationLiabilitiesLineItems
Namespace Prefix:	rgnx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Royalty monetization liabilities noncurrent.

+ References

No definition available.

+ Details

Name:	rgnx_RoyaltyMonetizationLiabilitiesNoncurrent
Namespace Prefix:	rgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69E

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69F
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69F

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-3

+ Details

Name:	us-gaap_AmortizationOfFinancingCostsAndDiscounts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Increase for accrued, but unpaid interest on the debt instrument for the period.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

+ Details

Name:	us-gaap_DebtInstrumentIncreaseAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of cash paid for royalties during the current period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 25
-Subparagraph (g)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-25

+ Details

Name:	us-gaap_PaymentsForRoyalties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_TypeOfArrangementAxis=rgnx_TwoThousandTwentyRoyaltyPurchaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=rgnx_HCRMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rgnx_TwoThousandTwentyFiveRoyaltyBondMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: