COLLABORATION, LICENSE AND MANUFACTURING AGREEMENTS	6 Months Ended
Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
COLLABORATION, LICENSE AND MANUFACTURING AGREEMENTS	3. COLLABORATION, LICENSE AND MANUFACTURING AGREEMENTS Myonexus Warrant Agreement In May 2018, the Company entered into a Warrant to Purchase Common Stock Agreement (“Warrant Agreement”) with Myonexus Therapeutics, Inc. (“Myonexus”). 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 at a pre-negotiated, fixed price plus sales-related and regulatory-related contingent payments. Prior to the exercise of the option to acquire Myonexus, the Company may be required to make additional development milestone payments to Myonexus of up to $45.0 million over an approximately two-year evaluation period. The up-front payment of $60.0 million to Myonexus provides the Company with rights to potential future benefits associated with Myonexus’s ongoing research and development activities, which have not reached technological feasibility and have no alternative future use. Accordingly, the up-front payment of $60.0 million was expensed as incurred and classified as research and development expense in the accompanying unaudited condensed consolidated statements of operations and comprehensive loss during the three and six months ended June 30, 2018. The additional development milestones payments of up to $45.0 million will also be recorded to research and development expense when (and if) incurred. The Company considered whether it would have to consolidate the operations of Myonexus and concluded that, while Myonexus is a variable interest entity, the Company is not the primary beneficiary as it does not have the power to direct the activities that would most significantly impact the economic performance of Myonexus. Brammer Manufacturing Agreement In June 2018, the Company entered into a Development, Commercial Manufacturing and Supply Agreement (“Brammer Manufacturing Agreement”), with Brammer Bio MA, LLC (“Brammer”). Pursuant to the terms of the Brammer Manufacturing Agreement, Brammer agreed to provide the Company with access to clinical and commercial manufacturing capacity for its gene therapy programs. As part of the Brammer Manufacturing Agreement, the Company will purchase product in batches from Brammer, subject to minimum and maximum annual purchase requirements. Further, the Company: (i) was required to make a $20.0 million advance payment to Brammer upon execution of the agreement, (ii) is required to make two non-refundable payments of $5.0 million each to Brammer in the third and fourth quarter of 2018 to be used in the specification, selection, and procurement of the related process equipment to be utilized under the agreement, and (iii) is required to make a $10.0 million quarterly capacity access fee payment to Brammer throughout the term of the agreement. However, through June 30, 2019, a reduced quarterly capacity access fee will be in effect as Brammer works towards achieving full capacity at its facility. In addition, one-tenth of the $20.0 million advance payment will be applied as a credit to the quarterly capacity access fees due and payable from July 1, 2019 through December 31, 2021, resulting in a net capacity access fee of $8.0 million. The term of the Brammer Manufacturing Agreement will continue for a period of six years following the first regulatory approval of a product manufactured under the agreement. The term will automatically renew for successive two years unless the Company notifies Brammer of its intention not to renew (no less than twenty-four months prior to the expiration of the term). The Company also has the ability to terminate the agreement prior to expiration but would be required to continue remitting capacity access fees to Brammer for up to eight additional quarters. The Company has determined that the Brammer Manufacturing Agreement does not contain an embedded lease because it does not convey the right to control the use of the facility or related equipment. This conclusion was based on the Company’s inability or right to control physical access to Brammer’s facility and the related equipment, and the ability of one or more parties, other than the Company, to take more than a minor amount of the output that will be produced during the term of the agreement. As of June 30, 2018, the $20.0 million advance payment was recorded as an other non-current asset in the accompanying unaudited condensed consolidated balance sheet. The advance payment will be amortized over its expected economic benefit to research and development expense, prior to regulatory approval of the related product, commencing upon the first batch delivery to the Company. Upon regulatory approval, amortization expense will be classified to cost of sales. In the event the Company does not expect services under the Brammer Manufacturing Agreement to be rendered, the capitalized advance payment will be charged to expense. The two $5.0 million process equipment fee payments will also be capitalized as an other asset when paid and amortized to expense in a manner similar to the advance payment described above. Capacity access fee payments made prior to the first batch delivery to the Company will also be capitalized as an other asset when paid and amortized to expense in a manner similar to the advance payment described above. Capacity access fee payments made subsequent to the first batch delivery to the Company will be expensed as incurred to research and development expense, prior to regulatory approval of the related product. Upon regulatory approval, the expense associated with capacity access fee payments will be classified to cost of sales.

3. COLLABORATION, LICENSE AND MANUFACTURING AGREEMENTS

Myonexus Warrant Agreement

In May 2018, the Company entered into a Warrant to Purchase Common Stock Agreement (“Warrant Agreement”) with Myonexus Therapeutics, Inc. (“Myonexus”). 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 at a pre-negotiated, fixed price plus sales-related and regulatory-related contingent payments. Prior to the exercise of the option to acquire Myonexus, the Company may be required to make additional development milestone payments to Myonexus of up to $45.0 million over an approximately two-year evaluation period.

The up-front payment of $60.0 million to Myonexus provides the Company with rights to potential future benefits associated with Myonexus’s ongoing research and development activities, which have not reached technological feasibility and have no alternative future use. Accordingly, the up-front payment of $60.0 million was expensed as incurred and classified as research and development expense in the accompanying unaudited condensed consolidated statements of operations and comprehensive loss during the three and six months ended June 30, 2018. The additional development milestones payments of up to $45.0 million will also be recorded to research and development expense when (and if) incurred.

The Company considered whether it would have to consolidate the operations of Myonexus and concluded that, while Myonexus is a variable interest entity, the Company is not the primary beneficiary as it does not have the power to direct the activities that would most significantly impact the economic performance of Myonexus.

Brammer Manufacturing Agreement

In June 2018, the Company entered into a Development, Commercial Manufacturing and Supply Agreement (“Brammer Manufacturing Agreement”), with Brammer Bio MA, LLC (“Brammer”). Pursuant to the terms of the Brammer Manufacturing Agreement, Brammer agreed to provide the Company with access to clinical and commercial manufacturing capacity for its gene therapy programs.

As part of the Brammer Manufacturing Agreement, the Company will purchase product in batches from Brammer, subject to minimum and maximum annual purchase requirements. Further, the Company: (i) was required to make a $20.0 million advance payment to Brammer upon execution of the agreement, (ii) is required to make two non-refundable payments of $5.0 million each to Brammer in the third and fourth quarter of 2018 to be used in the specification, selection, and procurement of the related process equipment to be utilized under the agreement, and (iii) is required to make a $10.0 million quarterly capacity access fee payment to Brammer throughout the term of the agreement. However, through June 30, 2019, a reduced quarterly capacity access fee will be in effect as Brammer works towards achieving full capacity at its facility. In addition, one-tenth of the $20.0 million advance payment will be applied as a credit to the quarterly capacity access fees due and payable from July 1, 2019 through December 31, 2021, resulting in a net capacity access fee of $8.0 million.

The term of the Brammer Manufacturing Agreement will continue for a period of six years following the first regulatory approval of a product manufactured under the agreement. The term will automatically renew for successive two years unless the Company notifies Brammer of its intention not to renew (no less than twenty-four months prior to the expiration of the term). The Company also has the ability to terminate the agreement prior to expiration but would be required to continue remitting capacity access fees to Brammer for up to eight additional quarters.

The Company has determined that the Brammer Manufacturing Agreement does not contain an embedded lease because it does not convey the right to control the use of the facility or related equipment. This conclusion was based on the Company’s inability or right to control physical access to Brammer’s facility and the related equipment, and the ability of one or more parties, other than the Company, to take more than a minor amount of the output that will be produced during the term of the agreement.

As of June 30, 2018, the $20.0 million advance payment was recorded as an other non-current asset in the accompanying unaudited condensed consolidated balance sheet. The advance payment will be amortized over its expected economic benefit to research and development expense, prior to regulatory approval of the related product, commencing upon the first batch delivery to the Company. Upon regulatory approval, amortization expense will be classified to cost of sales. In the event the Company does not expect services under the Brammer Manufacturing Agreement to be rendered, the capitalized advance payment will be charged to expense.

The two $5.0 million process equipment fee payments will also be capitalized as an other asset when paid and amortized to expense in a manner similar to the advance payment described above. Capacity access fee payments made prior to the first batch delivery to the Company will also be capitalized as an other asset when paid and amortized to expense in a manner similar to the advance payment described above. Capacity access fee payments made subsequent to the first batch delivery to the Company will be expensed as incurred to research and development expense, prior to regulatory approval of the related product. Upon regulatory approval, the expense associated with capacity access fee payments will be classified to cost of sales.