Significant Agreements - Additional Information (Detail)	1 Months Ended								8 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) Agreement	Aug. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Agreement	Oct. 31, 2015 USD ($)	Oct. 31, 2015 EUR (€)	May 31, 2014 USD ($) Target	Apr. 30, 2014 USD ($)	May 31, 2010 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 EUR (€)
License Agreement [Line Items]
Annual maintenance fee payable										$ 600,000	$ 100,000
License agreement, recorded research and development expenses										$ 31,670,000	25,462,000	$ 16,976,000
Regeneron Corporation [Member]
License Agreement [Line Items]
Agreement termination scenario description										Regeneron may terminate the agreement for convenience at any time on a target by target basis or in totality upon a 30-day notice. Each party can terminate the agreement if another party commits a material breach or material default in performance of its obligations and such breach or default is not cured within 60 days. The agreement is automatically terminated upon initiation of any bankruptcy proceedings, reorganization or dissolution of either party. The Company can terminate the agreement upon 30-day notice if Regeneron challenges the validity, scope or enforceability of any Company patent.
Potential target of collaborations | Target						8
Initial collaboration term						3 years
Additional collaboration term						5 years
Collaboration fee for exclusive worldwide license per target						$ 2,000,000
Potential milestone earnings						640,000,000
Reimbursement of research and development expense										35.00%
Regeneron Corporation [Member] | Development and Regulatory Milestone [Member]
License Agreement [Line Items]
Potential milestone earnings						$ 80,000,000
University of California [Member]
License Agreement [Line Items]
License fee paid								$ 100,000
Aggregate amount of milestone payments for one indication								$ 900,000
Additional milestone payments recognized										$ 0
Right and option to extend date to meet milestone, period								6 months
Right and option to extend date to meet milestone, description										The Company has the right and option to extend the date by which it must meet any milestone by six-months up to two times by paying an extension fee for each such extension.
Non-royalty licensing revenue, description										mid-teen percentage
Agreement termination scenario description										The Company may terminate this agreement without cause at any time upon 30 days’ prior written notice to the Regents. The Regents may terminate this agreement for a breach by the Company that remains uncured for 60 days, if the Company becomes insolvent, if the Company directly or through a third party files a claim that a licensed patent right is invalid or unenforceable or if the Company fails to meet or extend the date for meeting certain diligence milestones.
License agreement termination notice period										30 days
University of California [Member] | Maximum [Member]
License Agreement [Line Items]
Additional milestone payments for up to two additional indications								$ 500,000
University of California [Member] | Minimum [Member]
License Agreement [Line Items]
Annual royalty payment								$ 50,000
Editas Medicine Inc [Member]
License Agreement [Line Items]
Non-refundable upfront payment received		$ 1,000,000
Non-refundable upfront payment, obligation to fund research and development costs		500,000
Collaboration, option and license agreement fee receivable per indication		$ 1,000,000
Range of tiered royalties receivable on net sales										between the mid-single digits and low teens
Editas Medicine Inc [Member] | Maximum [Member]
License Agreement [Line Items]
Development and commercialization milestone payments receivable upon using proprietary vectors										mid-teen million dollar amount
Cornell University [Member]
License Agreement [Line Items]
Additional milestone payments recognized										$ 0
Agreement termination scenario description										Annapurna Therapeutics Limited may terminate any of these license agreements for convenience upon ninety days written notice. Cornell may terminate any of the license agreements for material breach if such breach is not cured within a specified number of days. Cornell may also terminate the HAE License Agreement and/or the Allergy License Agreement if Annapurna Therapeutics Limited commences any action and files a written claim asserting that any portion of the licensed patent rights invalid or unenforceable.
License agreement termination notice period										90 days
Number of license agreements | Agreement	3		3
Service fees payable			$ 13,300,000								$ 13,300,000
Service fees, payable period			4 years
Aggregate milestone payments and royalties on sales										$ 16,000,000
License agreement, accrued expenses	$ 800,000								$ 800,000	800,000
License agreement, recorded research and development expenses									1,800,000
Cornell University [Member] | Consultant [Member]
License Agreement [Line Items]
Annual compensation										300,000
Cornell University [Member] | Maximum [Member]
License Agreement [Line Items]
Annual maintenance fee payable										300,000
Cornell University [Member] | Minimum [Member]
License Agreement [Line Items]
Annual maintenance fee payable										30,000
REGENXBIO [Member]
License Agreement [Line Items]
Additional milestone payments recognized										$ 0
Agreement termination scenario description										Annapurna Therapeutics Limited may terminate this license agreement upon six months’ prior written notice. REGENXBIO may terminate this license agreement if Annapurna Therapeutics Limited is a specified number of days late in paying money due under the license agreement, or if Annapurna Therapeutics Limited, its affiliates, or any sublicensees become insolvent or, effective immediately, if they commence any action against REGENXBIO or its licensors to declare or render any claim of the licensed patent rights invalid or unenforceable. Either party may terminate this license agreement for material breach if such breach is not cured within a specified number of days.
License agreement termination notice period										6 months
License agreement, accrued expenses	$ 42,000								42,000	$ 42,000
License agreement, recorded expenses									$ 62,000
REGENXBIO [Member] | A1AT Deficiency/Allergy License Agreement [Member]
License Agreement [Line Items]
Agreement termination scenario description										Annapurna Therapeutics Limited may terminate this license agreement upon six months’ prior written notice. REGENXBIO may terminate this license agreement if Annapurna Therapeutics Limited is a specified number of days late in paying money due under the license agreement, or if Annapurna Therapeutics Limited, its affiliates, or any sublicensees become insolvent or, effective immediately, if they commence any action against REGENEXBIO or its licensors to declare or render any claim of the licensed patent rights invalid or unenforceable. Either party may terminate this license agreement for material breach if such breach is not cured within a specified number of days.
License agreement termination notice period										6 months
Aggregate milestone payments and royalties on sales				$ 20,000,000
REGENXBIO [Member] | Friedreich's Ataxia License Agreement [Member]
License Agreement [Line Items]
Aggregate milestone payments and royalties on sales							$ 13,850,000
Inserm Transfert [Member]
License Agreement [Line Items]
Additional milestone payments recognized										$ 0
Agreement termination scenario description										Annapurna may terminate this agreement upon 60 days’ prior written notice. Inserm may terminate this license agreement if Annapurna becomes the subject of a voluntary or involuntary petition in bankruptcy or fails to meet development milestones and such failure is not cured within a specified number of days. Inserm may also terminate the license granted to Annapurna in a given country if Annapurna (i) before regulatory approval of a product in any country, has ceased conducting any development of products in all countries for 12 consecutive months or (ii) after regulatory approval of a product in a given country, has ceased marketing such product in such country for 12 consecutive months.
License agreement termination notice period										60 days
Aggregate milestone payments and royalties on sales | €					€ 2,000,000
Inserm Transfert [Member] | Accrued Expenses and Other Current Liabilities [Member]
License Agreement [Line Items]
One-time payment due to termination of license agreement | €													€ 250,000