License and Collaboration Agreements - Additional Information (Detail)			1 Months Ended								12 Months Ended
	Jan. 11, 2022 USD ($)	Dec. 21, 2019 USD ($) shares	Nov. 30, 2021 USD ($)	Oct. 31, 2021 USD ($)	Jul. 31, 2021 USD ($)	Mar. 31, 2021 USD ($) shares	Nov. 30, 2019 USD ($) shares	Apr. 30, 2019 USD ($)	Jul. 31, 2017	Jun. 30, 2016 USD ($)	Dec. 31, 2022 USD ($) Milestone shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Aug. 31, 2022 USD ($)	Feb. 28, 2021 USD ($)	Feb. 29, 2020 USD ($)	Dec. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Aug. 08, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance costs				$ 26,500,000
Common stock fair value											$ 9,000	$ 9,000				$ 312,100,000
Product revenues, net											$ 843,769,000	$ 612,401,000	$ 455,865,000
Common stock, issued | shares											87,950,117	87,126,974
Impairment of equity investment											$ 2,575,000	$ 4,488,000	0
Contingent consideration											36,900,000	43,600,000
Intangible asset, net											7,578,000	14,239,000
Amortization of in-licensed rights											714,000	706,000	662,000
Unsecured Convertible Promissory Note And Warrants [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Unsecured debt														$ 200,000
Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty payments									8.00%
Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty payments									4.00%
Genethon [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense											$ 0	4,000,000.0	0
Up-front cash payment under development							$ 157,500,000
Up-front cash payment under sales milestone							$ 78,800,000
Up-front cash payment under development percentage							75.00%
Number of development milestone | Milestone											0
Other Licensed Products [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front cash payment under development percentage							25.00%
StrideBio, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock fair value							$ 29,400,000
Research and development expense											$ 0
Up-front cash payment under development							450,000,000.0
Up-front cash payment under sales milestone							835,000,000.0
Up-front cash expense							46,900,000
Up-front cash payment under agreements							$ 17,500,000
Common stock, issued | shares							301,980
Number of development milestone | Milestone											0
StrideBio, Inc. [Member] | Series B Preferred Stock [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Preferred stock purchase, shares | shares						200,000
Preferred stock purchase, value						$ 1,800,000
Impairment of equity investment											$ 2,000,000.0
Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Final exercise price								$ 178,300,000
Additional development milestone payments to be paid								$ 200,000,000.0
Contingent consideration											35,500,000	42,000,000.0
Lysogene S.A. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expenses charges	$ 800,000
Henogen SA [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expenses charges											17,100,000
Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense											$ 0
Number of development milestone | Milestone											0
BioMarin Pharmaceutical, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and sales milestone payments											$ 0
Intangible asset, net																				$ 6,600,000
Sales milestone payment recorded as an in-license right											0
Royalty expense											30,400,000	31,400,000	23,200,000
BioMarin Pharmaceutical, Inc. [Member] | AMONDYS 45 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory milestone payable															$ 10,000,000.0
BioMarin Pharmaceutical, Inc. [Member] | Intellectual Property
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amortization of in-licensed rights											2,700,000
BioMarin Pharmaceutical, Inc. [Member] | US [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment expiry period			2024-03
BioMarin Pharmaceutical, Inc. [Member] | EU [member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment expiry period			2024-12
BioMarin Pharmaceutical, Inc. [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and sales milestone payments			$ 50,000,000.0
Percentage of royalty payments			5.00%
BioMarin Pharmaceutical, Inc. [Member] | Maximum [Member] | Other Countries [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment expiry period			2024-12
BioMarin Pharmaceutical, Inc. [Member] | Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty payments			4.00%
University of Western Australia [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and sales milestone payments											0
Sales milestone payment recorded as an in-license right											0
Royalty expense											10,500,000	7,700,000	5,700,000
Carrying value of intangible assets											1,000,000.0
University of Western Australia [Member] | EXONDYS 51 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sales milestone payment recorded as an in-license right																					$ 1,000,000.0
University of Western Australia [Member] | VYONDYS 53 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sales milestone payment recorded as an in-license right																	$ 500,000
University of Western Australia [Member] | AMONDYS 45 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sales milestone payment recorded as an in-license right															$ 500,000
University of Western Australia [Member] | Maximum [Member] | EXONDYS 51 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payments to UWA on successful achievement of certain development and regulatory milestones										$ 26,000,000.0
Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment for option exercise											243,800,000	0	0
Development Milestone and Settlement Upfront Fee Recognized as Research and Development Expense											32,600,000	50,300,000	47,300,000
Contingent research milestone payments											6,000,000.0	3,000,000.0	0
Collaborative Arrangement | Research and Development Expense [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front and development milestone expenses											8,500,000
Collaborative Arrangement | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent research milestone payments											41,800,000
Development, regulatory, commercial milestone and up-front royalty payments											$ 3,200,000,000
Collaborative Arrangement | Roche Holding A.G. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds From License And Collaborative Agreement		$ 1,200,000,000
Issuance costs		$ 312,100,000
Stock Issued During Period Shares Collaboration and License Agreement | shares		2,500,000
Payment for option exercise		$ 485,000,000.0
Single combined performance obligation		348,700,000
Stock Options Exercised Or Expired | shares											0
Product revenues, net											$ 89,200,000	89,500,000	84,200,000
Deferred Revenue											574,200,000
Deferred Revenue, Current											89,200,000
Deferred Revenue Separate Material Options Right											485,000,000.0	485,000,000.0
Research and development expense											117,800,000	90,500,000	66,500,000
Collaboration receivable											41,800,000
Collaborative Arrangement | Roche Holding A.G. [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and Sales Milestones Payment Received		$ 1,700,000,000
Collaborative Arrangement | Genethon [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense											3,500,000	11,700,000	10,100,000
Up-front cash payment under development							$ 28,000,000.0
Equity Investment Agreement [Member] | Lysogene S.A. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments to be paid																		$ 102,800,000
Equity Investment Agreement [Member] | Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Investment change in carrying value											0	0	0
License Development And Option Agreement | Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred Revenue																			$ 42,000,000.0
Series A Preferred Stock Purchase Agreement | Lacerta Therapeutics [Member] | Series A Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front payment | shares																			4,500,000
Series A Preferred Stock Purchase Agreement | Lacerta Therapeutics [Member] | Other Noncurrent Assets [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred Revenue																			$ 30,000,000.0
License And Purchase Agreement | Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred Revenue																			$ 38,000,000.0
Nationwide License Agreement [Member] | Nationwide Children's Hospital [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments to be paid											0
Sublicense payment					$ 38,000,000.0
Sales milestone payment recorded as an in-license right											$ 0
Nationwide License Agreement [Member] | Nationwide Children's Hospital [Member] | Research and Development Expense [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense payment												$ 28,700,000	$ 9,300,000