Subsequent Events	9 Months Ended
Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events In connection with the sale of the Commercial Business, the Company retained the right to receive net milestone payments that may become payable related to the development and commercialization of ONIVYDE for up to $33.0 million pursuant to the Baxalta Agreement. In October 2018, the Company received a payment of $5.0 million from Ipsen against the milestone related to the first patient dosed in a pivotal clinical trial of ONIVYDE in an indication other than pancreatic cancer as a result of the commencement of a multi-part study that Ipsen and Servier are conducting in patients with small-cell lung cancer. The Company expects to receive the remaining $5.0 million for such milestone if and when a decision is made to progress to the randomized part of the study focused on efficacy. To date, the Company has received $28.0 million of the potential $33.0 million in milestone payments under the Baxalta Agreement. On October 19, 2018, the Company announced the termination of its global, open-label, biomarker-selected, Phase 2 randomized SHERLOC clinical trial evaluating MM-121 (seribantumab) in combination with docetaxel in patients with heregulin positive non-small cell lung cancer. The decision to terminate the SHERLOC clinical trial was made based on an interim analysis triggered by the occurrence of 75% of events required for trial completion, which demonstrated that the addition of MM-121 to docetaxel did not improve progression free survival over docetaxel alone in this patient population. As a result of the decision to terminate the SHERLOC clinical trial, the Company does not meet the prerequisite funding conditions for drawing the two additional term loan advances under the Loan Agreement (see Note 5, “Notes Payable”), which provided for, at the Company’s option, two additional term loan advances of $5.0 million each upon the occurrence of certain funding conditions prior to December 31, 2018 and December 31, 2019, respectively. On November 7, 2018, based on the results of the interim analysis of its randomized Phase 2 SHERLOC study that were announced on October 19, 2018, the Company announced it is discontinuing development of all ongoing MM-121 programs, including terminating its global, double-blinded, placebo-controlled, biomarker-selected, Phase 2 randomized SHERBOC clinical trial evaluating MM-121 in combination with fulvestrant in patients with heregulin positive, hormone receptor positive, ErbB2 (HER2) negative, metastatic breast cancer. On November 7, 2018, the Company announced that it was implementing a reduction in headcount as part of a corporate restructuring, after which the Company expects to have approximately 27 employees. The corporate restructuring follows a comprehensive review of the Company’s drug candidate pipeline. The Company estimates it will incur expenses for one-time termination benefits in connection with this corporate restructuring of approximately $1.5 million to $1.8 million for employee severance, benefits and related costs. The reduction in headcount is expected to be completed by February 2019.

12. Subsequent Events

In connection with the sale of the Commercial Business, the Company retained the right to receive net milestone payments that may become payable related to the development and commercialization of ONIVYDE for up to $33.0 million pursuant to the Baxalta Agreement. In October 2018, the Company received a payment of $5.0 million from Ipsen against the milestone related to the first patient dosed in a pivotal clinical trial of ONIVYDE in an indication other than pancreatic cancer as a result of the commencement of a multi-part study that Ipsen and Servier are conducting in patients with small-cell lung cancer. The Company expects to receive the remaining $5.0 million for such milestone if and when a decision is made to progress to the randomized part of the study focused on efficacy. To date, the Company has received $28.0 million of the potential $33.0 million in milestone payments under the Baxalta Agreement.

On October 19, 2018, the Company announced the termination of its global, open-label, biomarker-selected, Phase 2 randomized SHERLOC clinical trial evaluating MM-121 (seribantumab) in combination with docetaxel in patients with heregulin positive non-small cell lung cancer. The decision to terminate the SHERLOC clinical trial was made based on an interim analysis triggered by the occurrence of 75% of events required for trial completion, which demonstrated that the addition of MM-121 to docetaxel did not improve progression free survival over docetaxel alone in this patient population.

As a result of the decision to terminate the SHERLOC clinical trial, the Company does not meet the prerequisite funding conditions for drawing the two additional term loan advances under the Loan Agreement (see Note 5, “Notes Payable”), which provided for, at the Company’s option, two additional term loan advances of $5.0 million each upon the occurrence of certain funding conditions prior to December 31, 2018 and December 31, 2019, respectively.

On November 7, 2018, based on the results of the interim analysis of its randomized Phase 2 SHERLOC study that were announced on October 19, 2018, the Company announced it is discontinuing development of all ongoing MM-121 programs, including terminating its global, double-blinded, placebo-controlled, biomarker-selected, Phase 2 randomized SHERBOC clinical trial evaluating MM-121 in combination with fulvestrant in patients with heregulin positive, hormone receptor positive, ErbB2 (HER2) negative, metastatic breast cancer.

On November 7, 2018, the Company announced that it was implementing a reduction in headcount as part of a corporate restructuring, after which the Company expects to have approximately 27 employees. The corporate restructuring follows a comprehensive review of the Company’s drug candidate pipeline. The Company estimates it will incur expenses for one-time termination benefits in connection with this corporate restructuring of approximately $1.5 million to $1.8 million for employee severance, benefits and related costs. The reduction in headcount is expected to be completed by February 2019.