Subsequent Event	6 Months Ended
Jun. 30, 2019
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event miniCEP290 License Agreement On July 22, 2019, the Company entered into an Exclusive License Agreement (the “miniCEP290 License Agreement”) with the University of Massachusetts (“UMass”). The Company entered into the miniCEP290 License Agreement by exercising its exclusive option rights under an option agreement and a sponsored research agreement that the Company previously entered into with UMass in February 2018. Under the miniCEP290 License Agreement, UMass granted the Company a worldwide, exclusive license under specified patent rights and specified biological materials and a non-exclusive license under specified know-how to make, have made, use, offer to sell, sell, have sold and import products for the treatment of diseases associated with mutations in the CEP290 gene, including LCA10. The Company may grant sublicenses of the licensed patent rights and know-how without the consent of UMass. The Company has agreed to use diligent efforts to develop licensed products and to introduce such licensed products into the commercial market. Subject to obtaining marketing approval, the Company agreed to make any approved licensed product reasonably available to the public. In addition, the Company has agreed to meet specified development and regulatory milestones with respect to a licensed product by specified dates, as the same may be extended under the terms of the miniCEP290 License Agreement. Financial Terms The Company has agreed to pay UMass a $0.4 million upfront license fee upon execution of the miniCEP290 License Agreement. In addition, the Company has agreed to issue to UMass 75,000 shares of common stock of the Company, par value $0.001 per share (“Common Stock”), promptly following execution of the miniCEP290 License Agreement pursuant to an exemption from registration afforded by Section 4(a)(2) of the Securities Act of 1933, as amended. The Company has also agreed to pay UMass an annual license maintenance fee in the low double-digit thousands of dollars, which fee will be payable on an annual basis until the expiration of the royalty term for the licensed products. Furthermore, the Company has agreed to reimburse UMass for the costs and expenses of patent prosecution and maintenance related to the licensed patent rights. The Company has further agreed to pay UMass up to an aggregate of $14.75 million in cash and issue up to 75,000 shares of Common Stock if the Company achieves specified clinical and regulatory milestones with respect to a licensed product. In addition, the Company has agreed to pay UMass up to an aggregate of $48.0 million if the Company achieves specified commercial sales milestones with respect to a licensed product. The Company is also obligated to pay UMass royalties at a low single-digit percentage of net sales of licensed products. The Company's obligation to pay royalties under the miniCEP290 License Agreement will continue on a licensed product-by-licensed product and country-by-country basis until the later of: (a) the expiration of the last-to-expire licensed patent rights covering the sale of the applicable licensed product in the country of sale, or (b) 10 years from the first commercial sale of the applicable licensed product in the country of sale. Beginning with the calendar year following receipt of marketing approval for a licensed product, the Company is also obligated to pay certain minimum royalties, not to exceed an amount in the mid-double-digit thousands of dollars on an annual basis, which minimum royalties are creditable against the Company’s royalty obligation with respect to net sales of licensed products due in the year the minimum royalty is paid. If the Company or any of its affiliates sublicenses any of the licensed patent rights or know-how to a third party, the Company will be obligated to pay UMass a high single-digit to a mid-tens percentage of the consideration received in exchange for such sublicense, with the applicable percentage based upon the stage of development of the licensed products at the time the Company or the applicable affiliate enters into the sublicense. If the Company receives a rare pediatric disease priority review voucher (a “priority review voucher”) from the FDA in connection with obtaining marketing approval for a licensed product, and the Company subsequently uses such priority review voucher in connection with a different product candidate outside the scope of the miniCEP290 License Agreement, the Company will be obligated to pay UMass a low-tens percentage of the fair market value of the priority review voucher at the time of approval of such product candidate and a low-twenties percentage of the fair market value of the priority review voucher at the time of achievement of a specified commercial sales milestone for such other product candidate. In addition, if the Company sells such a priority review voucher to a third party, the Company will be obligated to pay UMass a low-thirties percentage of any consideration received from such third party in connection with such sale. Term and Termination The miniCEP290 License Agreement, unless earlier terminated by the Company or UMass, will expire upon the expiration of the Company's obligation to pay royalties to UMass on net sales of licensed products. The Company may terminate the miniCEP290 License Agreement at any time for any reason upon prior written notice to UMass. The Company may also terminate the miniCEP290 License Agreement if UMass materially breaches the miniCEP290 License Agreement and does not cure such breach within a specified cure period. UMass may terminate the miniCEP290 License Agreement if the Company materially breaches the miniCEP290 License Agreement and does not cure such breach within a specified cure period. Following any termination of the miniCEP290 License Agreement prior to expiration of the term of the miniCEP290 License Agreement, all rights to the licensed patent rights and know-how that UMass granted to the Company will revert to UMass. Other Provisions The miniCEP290 License Agreement contains patent prosecution and maintenance, indemnification and dispute resolution provisions that are customary for agreements of this kind.

Subsequent Event

miniCEP290 License Agreement

On July 22, 2019, the Company entered into an Exclusive License Agreement (the “miniCEP290 License Agreement”) with the University of Massachusetts (“UMass”). The Company entered into the miniCEP290 License Agreement by exercising its exclusive option rights under an option agreement and a sponsored research agreement that the Company previously entered into with UMass in February 2018. Under the miniCEP290 License Agreement, UMass granted the Company a worldwide, exclusive license under specified patent rights and specified biological materials and a non-exclusive license under specified know-how to make, have made, use, offer to sell, sell, have sold and import products for the treatment of diseases associated with mutations in the CEP290 gene, including LCA10. The Company may grant sublicenses of the licensed patent rights and know-how without the consent of UMass.

The Company has agreed to use diligent efforts to develop licensed products and to introduce such licensed products into the commercial market. Subject to obtaining marketing approval, the Company agreed to make any approved licensed product reasonably available to the public. In addition, the Company has agreed to meet specified development and regulatory milestones with respect to a licensed product by specified dates, as the same may be extended under the terms of the miniCEP290 License Agreement.

Financial Terms

The Company has agreed to pay UMass a $0.4 million upfront license fee upon execution of the miniCEP290 License Agreement. In addition, the Company has agreed to issue to UMass 75,000 shares of common stock of the Company, par value $0.001 per share (“Common Stock”), promptly following execution of the miniCEP290 License Agreement pursuant to an exemption from registration afforded by Section 4(a)(2) of the Securities Act of 1933, as amended.

The Company has also agreed to pay UMass an annual license maintenance fee in the low double-digit thousands of dollars, which fee will be payable on an annual basis until the expiration of the royalty term for the licensed products. Furthermore, the Company has agreed to reimburse UMass for the costs and expenses of patent prosecution and maintenance related to the licensed patent rights.

The Company has further agreed to pay UMass up to an aggregate of $14.75 million in cash and issue up to 75,000 shares of Common Stock if the Company achieves specified clinical and regulatory milestones with respect to a licensed product. In addition, the Company has agreed to pay UMass up to an aggregate of $48.0 million if the Company achieves specified commercial sales milestones with respect to a licensed product.

The Company is also obligated to pay UMass royalties at a low single-digit percentage of net sales of licensed products. The Company's obligation to pay royalties under the miniCEP290 License Agreement will continue on a licensed product-by-licensed product and country-by-country basis until the later of: (a) the expiration of the last-to-expire licensed patent rights covering the sale of the applicable licensed product in the country of sale, or (b) 10 years from the first commercial sale of the applicable licensed product in the country of sale. Beginning with the calendar year following receipt of marketing approval for a licensed product, the Company is also obligated to pay certain minimum royalties, not to exceed an amount in the mid-double-digit thousands of dollars on an annual basis, which minimum royalties are creditable against the Company’s royalty obligation with respect to net sales of licensed products due in the year the minimum royalty is paid.

If the Company or any of its affiliates sublicenses any of the licensed patent rights or know-how to a third party, the Company will be obligated to pay UMass a high single-digit to a mid-tens percentage of the consideration received in exchange for such sublicense, with the applicable percentage based upon the stage of development of the licensed products at the time the Company or the applicable affiliate enters into the sublicense.

If the Company receives a rare pediatric disease priority review voucher (a “priority review voucher”) from the FDA in connection with obtaining marketing approval for a licensed product, and the Company subsequently uses such priority review voucher in connection with a different product candidate outside the scope of the miniCEP290 License Agreement, the Company will be obligated to pay UMass a low-tens percentage of the fair market value of the priority review voucher at the time of approval of such product candidate and a low-twenties percentage of the fair market value of the priority review voucher at the time of achievement of a specified commercial sales milestone for such other product candidate. In addition, if the Company sells such a priority review voucher to a third party, the Company will be obligated to pay UMass a low-thirties percentage of any consideration received from such third party in connection with such sale.

Term and Termination

The miniCEP290 License Agreement, unless earlier terminated by the Company or UMass, will expire upon the expiration of the Company's obligation to pay royalties to UMass on net sales of licensed products. The Company may terminate the miniCEP290 License Agreement at any time for any reason upon prior written notice to UMass. The Company may also terminate the miniCEP290 License Agreement if UMass materially breaches the miniCEP290 License Agreement and does not cure such breach within a specified cure period.

UMass may terminate the miniCEP290 License Agreement if the Company materially breaches the miniCEP290 License Agreement and does not cure such breach within a specified cure period.

Following any termination of the miniCEP290 License Agreement prior to expiration of the term of the miniCEP290 License Agreement, all rights to the licensed patent rights and know-how that UMass granted to the Company will revert to UMass.

Other Provisions

The miniCEP290 License Agreement contains patent prosecution and maintenance, indemnification and dispute resolution provisions that are customary for agreements of this kind.