LICENSE AND COLLABORATION AGREEMENTS	3 Months Ended
Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
LICENSE AND COLLABORATION AGREEMENTS	3. LICENSE AND COLLABORATION AGREEMENTS Myonexus Therapeutics On May 3, 2018, the Company entered into a Warrant to Purchase Common Stock Agreement (“Warrant Agreement”) with Myonexus Therapeutics, Inc. (“Myonexus”), a clinical-stage gene therapy biotechnology company that was developing gene therapies for Limb-Girdle muscular dystrophies (“LGMD”). Pursuant to the terms of the Warrant Agreement, the Company made an up-front payment of $60.0 million to purchase an exclusive option to acquire Myonexus for $200.0 million plus sales-related and regulatory-related contingent payments. On February 27, 2019, the Company announced that it exercised the exclusive option to acquire Myonexus. The final exercise price as negotiated between the Company and Myonexus was $165.0 million. In addition, the Company incurred transaction fees associated with the exercise of approximately $8.7 million. The Company may also be required to make up to $200.0 million in additional payments to selling shareholders of Myonexus based on the achievement of certain milestones. The acquisition was completed on April 4, 2019. As a result, the Company is expected to recognize approximately $168.7 million in in-process research and development expense during the three months ended June 30, 2019. Milestone Obligations The Company has license and collaboration agreements in place for which it could be obligated to pay, in addition to the payment of up-front fees upon execution of the agreements, certain milestone payments as a product candidate proceeds from the submission of an investigational new drug application through approval for commercial sale and beyond. As of March 31, 2019, the Company may be obligated to make up to $555.8 million of future development, regulatory, commercial, and up-front royalty milestone payments associated with its license and collaboration agreements. For the three months ended March 31, 2019, the Company recognized milestone payments of $1.1 million as research and development expense in the accompanying unaudited condensed consolidated statement of operations and comprehensive loss, with no such activity for the three months ended March 31, 2018.

LICENSE AND COLLABORATION AGREEMENTS

3 Months Ended

Mar. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

3. LICENSE AND COLLABORATION AGREEMENTS

Myonexus Therapeutics

On May 3, 2018, the Company entered into a Warrant to Purchase Common Stock Agreement (“Warrant Agreement”) with Myonexus Therapeutics, Inc. (“Myonexus”), a clinical-stage gene therapy biotechnology company that was developing gene therapies for Limb-Girdle muscular dystrophies (“LGMD”). Pursuant to the terms of the Warrant Agreement, the Company made an up-front payment of $60.0 million to purchase an exclusive option to acquire Myonexus for $200.0 million plus sales-related and regulatory-related contingent payments.

On February 27, 2019, the Company announced that it exercised the exclusive option to acquire Myonexus. The final exercise price as negotiated between the Company and Myonexus was $165.0 million. In addition, the Company incurred transaction fees associated with the exercise of approximately $8.7 million. The Company may also be required to make up to $200.0 million in additional payments to selling shareholders of Myonexus based on the achievement of certain milestones. The acquisition was completed on April 4, 2019. As a result, the Company is expected to recognize approximately $168.7 million in in-process research and development expense during the three months ended June 30, 2019.

Milestone Obligations

The Company has license and collaboration agreements in place for which it could be obligated to pay, in addition to the payment of up-front fees upon execution of the agreements, certain milestone payments as a product candidate proceeds from the submission of an investigational new drug application through approval for commercial sale and beyond. As of March 31, 2019, the Company may be obligated to make up to $555.8 million of future development, regulatory, commercial, and up-front royalty milestone payments associated with its license and collaboration agreements. For the three months ended March 31, 2019, the Company recognized milestone payments of $1.1 million as research and development expense in the accompanying unaudited condensed consolidated statement of operations and comprehensive loss, with no such activity for the three months ended March 31, 2018.