Subsequent Events	6 Months Ended
Subsequent Events	Jun. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events which may require adjustment to or disclosure in the accompanying unaudited condensed consolidated financial statements and has concluded that there are no subsequent events or transactions that occurred subsequent to the balance sheet date that would require recognition or disclosure in the accompanying unaudited condensed consolidated financial statements, except as noted below. Ipsen Collaboration, License, and Option Agreement On July 30, 2021, the Company entered into a Collaboration, Option and License Agreement (the “Ipsen Collaboration Agreement”) with IPSEN BIOPHARM LIMITED (“Ipsen”). Pursuant to the Ipsen Collaboration Agreement, the Company granted to Ipsen exclusive access and options to license SNA based therapeutics arising from two collaboration programs related to the treatment of Huntington’s disease and Angelman syndrome, respectively. Each such license would grant to Ipsen exclusive, royalty-bearing, sublicensable, worldwide rights to develop, manufacture, use and commercialize such SNA therapeutics. Upon written notice to the Company, Ipsen may exercise its option during the corresponding collaboration program’s applicable option exercise period, (each, an “Option Exercise Period”). Under the terms of the Ipsen Collaboration Agreement, the Company will conduct discovery and development in two collaboration programs for Huntington’s disease and Angelman syndrome. The Company shall be solely responsible for all costs and expenses of conducting each collaboration program through the selection of SNA therapeutic candidates for further development (“Selection”), and Ipsen shall be responsible for all costs and expenses of all additional activities that are necessary to enable the first filing of an investigational new drug application (“IND”) for each proposed product candidate. In the event that Ipsen exercises an option, Ipsen will be responsible for further development from the license effective date and commercialization of the corresponding licensed product. Under the terms of the Ipsen Collaboration Agreement, the Company will receive an upfront payment of $20,000 (the “Ipsen Upfront Payment”), and, depending on the timing when Ipsen exercises its option right in a collaboration program, Ipsen will pay to the Company an option exercise fee equal to $10,000 (if exercised within the Option Exercise Period after the Selection) or $25,000 (if exercised within the Option Exercise Period that begins after the first Option Exercise Period and ends after IND filing) for each collaboration program. Ipsen will pay a pre-clinical milestone of $5,000 for each collaboration program upon achievement of such milestone regardless of whether an option is exercised. In addition to the option exercise fees and the pre-clinical milestones described above, if Ipsen exercises an option for a program, development and regulatory milestones will be payable for that program upon the initiation of certain clinical trials, and the filing for processing by the FDA in the United States and by 2 additional regulators outside the United States of a marketing application for review, per program, with an aggregate total of up to $180,000 if both options are exercised. Commercial milestones will be payable for that program upon first commercial sale of a licensed product in certain jurisdictions and the achievement of specified aggregate sales thresholds for all licensed products from that program, with an aggregate total of up to $762,000 if both options are exercised. In the event a therapeutic candidate subject to the collaboration results in commercial sales, the Company is eligible to receive tiered royalties at percentages ranging from the mid-single digits to the mid-teens on future net product sales of such commercialized therapeutic candidates. A percentage of the aforementioned payments will be due to NU upon receipt, pursuant to the terms of the Company’s existing license agreements with NU (see Note 13, Commitment and Contingencies, for more information on the Northwestern University License Agreements). In connection with the receipt of the Ipsen Upfront Payment, the Company will incur $3,000 in license fees payable to NU under the terms of the Northwestern License Agreements. The Ipsen Collaboration Agreement will remain in effect, unless earlier terminated, until (a) the expiration of the later-to-expire option exercise period, if Ipsen does not exercise either option, or (b) the expiration of the last-to-expire royalty term for any licensed product in such country on a licensed product-by-licensed product and country-by-country basis, if Ipsen exercises one or both options. Upon expiration of the royalty term with respect to a particular licensed product in a country, the license for such product in such country will convert to a fully-paid, irrevocable and perpetual license. The Ipsen Collaboration Agreement also contains customary provisions for termination by either party, including in the event of breach of the Ipsen Collaboration Agreement, subject to cure, and by the Company upon a challenge of the licensed patents, subject, in certain cases, to customary reversion rights. Upon termination of the Ipsen Collaboration Agreement by the Company for Ipsen’s breach or bankruptcy, all licenses granted by the Company to Ipsen will terminate. The Ipsen Collaboration Agreement includes customary representations and warranties on behalf of both the Company and Ipsen. The Ipsen Collaboration Agreement also provides for customary mutual indemnities. In addition, the Ipsen Collaboration Agreement imposes certain exclusivity obligations on Ipsen and the Company, respectively, with respect to the development, use, manufacture and commercialization of oligonucleotide-based therapeutic targeting the same targets in the collaboration programs and/or certain other specific targets. Either party may assign the Ipsen Collaboration Agreement or delegate its obligations to an affiliate or to a successor to substantially all of the business to which the Ipsen Collaboration Agreement relates without the consent of the other party. In connection with the entry into the Ipsen Collaboration Agreement, the Company, Ipsen and NU entered into a side letter to the Northwestern University License Agreements (the “Side Letter”). Pursuant to the Side Letter, the parties thereto clarified certain provisions of the Northwestern University License Agreements as they apply to the sublicenses granted to Ipsen pursuant to the Ipsen Collaboration Agreement, including providing for the survival of Ipsen’s sublicense to the applicable NU intellectual property rights should the Northwestern University License Agreements terminate or if the Company’s licenses to such intellectual property rights are rendered non-exclusive in accordance with the Northwestern University License Agreements (other than as a result of an act or omission on the part of Ipsen or any of its Affiliates or sublicensees). Additionally, the Side Letter clarified Ipsen’s rights to grant further sublicenses under such intellectual property rights granted to the Company pursuant to the Northwestern University License Agreements.