Consolidated Subsidiaries	12 Months Ended
Dec. 31, 2015
Text Block [Abstract]
Consolidated Subsidiaries	7. Consolidated Subsidiaries Silver Creek Pharmaceuticals, Inc. On August 20, 2010, the Company acquired a controlling interest in Silver Creek. The Company has concluded that Silver Creek is a variable interest entity and the Company is the primary beneficiary. The Company has the ability to direct the activities of Silver Creek through its ownership percentage and through the board of director seats controlled by the Company and its de facto agents. As such, Silver Creek is consolidated by the Company. In December 2012, as described in Note 11, “Borrowings,” Silver Creek entered into a Note Purchase Agreement pursuant to which it issued convertible notes to various lenders in aggregate principal amounts of $1.6 million in December 2012, $0.3 million in February 2013 and $0.6 million in December 2013. As of December 31, 2013, these outstanding borrowings and related accrued interest of $2.6 million converted to shares of Silver Creek Series A preferred stock at the Series A preferred stock value of $1.00 per share. As a result of changes to the ownership composition of Silver Creek as of December 31, 2013, the non-controlling interest in Silver Creek increased by $0.8 million. During the year ended December 31, 2014, Silver Creek issued convertible notes to various lenders in the aggregate principal amount of $1.0 million. As of December 31, 2014, these outstanding borrowings and an immaterial amount of related accrued interest converted to shares of Silver Creek Series A preferred stock at the Series A preferred stock value of $1.00 per share. As a result of changes to the ownership composition of Silver Creek as of December 31, 2014, the non-controlling interest in Silver Creek increased by approximately $0.4 million. During the year ended December 31, 2015, Silver Creek issued and sold a total of 1.6 million shares of Silver Creek Series B preferred stock at a price per share of $1.35 to investors and received net proceeds of $2.1 million, after deducting issuance costs. As a result of changes to the ownership composition of Silver Creek as of December 31, 2015, the non-controlling interest in Silver Creek increased by approximately $0.9 million. As of December 31, 2015 and 2014, the Company owned approximately 56% and 60% of the voting stock of Silver Creek, respectively, and recorded a non-controlling interest of approximately $0.2 million and $0.1 million, respectively, as a component of mezzanine equity on the Company’s consolidated balance sheets based on the terms of the Silver Creek Series A and Series B preferred stock. As of December 31, 2015, the Company consolidated Silver Creek’s total assets and total liabilities of $0.8 million and $0.2 million, respectively. As of December 31, 2014, the Company consolidated Silver Creek’s total assets and total liabilities of $0.3 million and $0.2 million, respectively. As of December 31, 2015 and 2014, the Company’s unrestricted cash and cash equivalents balance includes $0.7 million and $0.3 million, respectively, of cash and cash equivalents held by Silver Creek. The cash and cash equivalents held by Silver Creek as of December 31, 2015 are designated for the operations of Silver Creek. Merrimack Pharmaceuticals (Bermuda) Ltd. Merrimack Pharmaceuticals (Bermuda) Ltd. was incorporated in Bermuda during 2011 and merged with and into the Company during the third quarter of 2014.

7. Consolidated Subsidiaries

Silver Creek Pharmaceuticals, Inc.

On August 20, 2010, the Company acquired a controlling interest in Silver Creek. The Company has concluded that Silver Creek is a variable interest entity and the Company is the primary beneficiary. The Company has the ability to direct the activities of Silver Creek through its ownership percentage and through the board of director seats controlled by the Company and its de facto agents. As such, Silver Creek is consolidated by the Company.

In December 2012, as described in Note 11, “Borrowings,” Silver Creek entered into a Note Purchase Agreement pursuant to which it issued convertible notes to various lenders in aggregate principal amounts of $1.6 million in December 2012, $0.3 million in February 2013 and $0.6 million in December 2013. As of December 31, 2013, these outstanding borrowings and related accrued interest of $2.6 million converted to shares of Silver Creek Series A preferred stock at the Series A preferred stock value of $1.00 per share. As a result of changes to the ownership composition of Silver Creek as of December 31, 2013, the non-controlling interest in Silver Creek increased by $0.8 million.

During the year ended December 31, 2014, Silver Creek issued convertible notes to various lenders in the aggregate principal amount of $1.0 million. As of December 31, 2014, these outstanding borrowings and an immaterial amount of related accrued interest converted to shares of Silver Creek Series A preferred stock at the Series A preferred stock value of $1.00 per share. As a result of changes to the ownership composition of Silver Creek as of December 31, 2014, the non-controlling interest in Silver Creek increased by approximately $0.4 million.

During the year ended December 31, 2015, Silver Creek issued and sold a total of 1.6 million shares of Silver Creek Series B preferred stock at a price per share of $1.35 to investors and received net proceeds of $2.1 million, after deducting issuance costs. As a result of changes to the ownership composition of Silver Creek as of December 31, 2015, the non-controlling interest in Silver Creek increased by approximately $0.9 million.

As of December 31, 2015 and 2014, the Company owned approximately 56% and 60% of the voting stock of Silver Creek, respectively, and recorded a non-controlling interest of approximately $0.2 million and $0.1 million, respectively, as a component of mezzanine equity on the Company’s consolidated balance sheets based on the terms of the Silver Creek Series A and Series B preferred stock.

As of December 31, 2015, the Company consolidated Silver Creek’s total assets and total liabilities of $0.8 million and $0.2 million, respectively. As of December 31, 2014, the Company consolidated Silver Creek’s total assets and total liabilities of $0.3 million and $0.2 million, respectively. As of December 31, 2015 and 2014, the Company’s unrestricted cash and cash equivalents balance includes $0.7 million and $0.3 million, respectively, of cash and cash equivalents held by Silver Creek. The cash and cash equivalents held by Silver Creek as of December 31, 2015 are designated for the operations of Silver Creek.

Merrimack Pharmaceuticals (Bermuda) Ltd.

Merrimack Pharmaceuticals (Bermuda) Ltd. was incorporated in Bermuda during 2011 and merged with and into the Company during the third quarter of 2014.