Related Parties	3 Months Ended
Mar. 31, 2020
Related Party Transactions [Abstract]
Related Parties	Related Parties A member of the Company’s board of directors is a founding director and the current president of the Broad. In November 2015, the Company entered into the Broad Agreement with the Broad (see Note 8) and, as consideration, the Company granted 60,000 shares of restricted common stock to the Broad, which were determined to have a fair value of $0.1 million. Additionally, the Company must pay the Broad immaterial annual license maintenance fees. At the time the Company entered into the Broad Agreement, the Company reimbursed the Broad $0.6 million for a portion of past patent expenses and, under the terms of the license agreement, the Company is required to reimburse Broad for future patent expenses related to patents covered by the license agreement. The Company could be obligated to make up to $12.6 million of developmental milestone payments to the Broad if certain development milestones are achieved over the term of the license agreement. Additionally, under the terms of the license agreement, the Company could be obligated to make up to an aggregate of $97.5 million of payments upon the achievement of specified sales milestones and to pay tiered royalties of low to mid single-digit percentages on net sales of products licensed under the agreement. The Company is required to pay the Broad a low double-digit percentage of any consideration received by the Company from a sublicensee in consideration for a sublicense. No developmental or commercial milestones have been achieved to date. In August 2016, the Company entered into a license agreement with the DFCI in connection with the development of licensed products referred to in the Broad Agreement. As consideration, the Company granted 120,000 shares of restricted common stock to the Broad, which were determined to have a fair value of $0.2 million. In June 2018, to align with institutional policies in place between the Broad, DFCI and MGH, the DFCI and MGH transferred certain of the shares of restricted common stock that they had previously received to the Broad. The Company recorded expenses related to payments to the Broad of $0.6 million and $0.5 million during the three months ended March 31, 2020 and 2019, respectively. At March 31, 2020 and December 31, 2019, the Company had $0.7 million and $0.3 million in accounts payable and accrued expenses due to the Broad, respectively.

Related Parties

A member of the Company’s board of directors is a founding director and the current president of the Broad. In November 2015, the Company entered into the Broad Agreement with the Broad (see Note 8) and, as consideration, the Company granted 60,000 shares of restricted common stock to the Broad, which were determined to have a fair value of $0.1 million. Additionally, the Company must pay the Broad immaterial annual license maintenance fees. At the time the Company entered into the Broad Agreement, the Company reimbursed the Broad $0.6 million for a portion of past patent expenses and, under the terms of the license agreement, the Company is required to reimburse Broad for future patent expenses related to patents covered by the license agreement. The Company could be obligated to make up to $12.6 million of developmental milestone payments to the Broad if certain development milestones are achieved over the term of the license agreement. Additionally, under the terms of the license agreement, the Company could be obligated to make up to an aggregate of $97.5 million of payments upon the achievement of specified sales milestones and to pay tiered royalties of low to mid single-digit percentages on net sales of products licensed under the agreement. The Company is required to pay the Broad a low double-digit percentage of any consideration received by the Company from a sublicensee in consideration for a sublicense. No developmental or commercial milestones have been achieved to date.

In August 2016, the Company entered into a license agreement with the DFCI in connection with the development of licensed products referred to in the Broad Agreement. As consideration, the Company granted 120,000 shares of restricted common stock to the Broad, which were determined to have a fair value of $0.2 million. In June 2018, to align with institutional policies in place between the Broad, DFCI and MGH, the DFCI and MGH transferred certain of the shares of restricted common stock that they had previously received to the Broad.

The Company recorded expenses related to payments to the Broad of $0.6 million and $0.5 million during the three months ended March 31, 2020 and 2019, respectively. At March 31, 2020 and December 31, 2019, the Company had $0.7 million and $0.3 million in accounts payable and accrued expenses due to the Broad, respectively.