Significant Agreements	12 Months Ended
Dec. 31, 2011
Significant Agreements Disclosure [Text Block]	(18) Significant Agreements Sigma-Tau Group The Company sold its specialty pharmaceutical business to Klee Pharmaceuticals Inc. (now known as Sigma-Tau PharmaSource, Inc.), Defiante Farmacêutica, S.A and sigma-tau Finanziaria S.p.A. (collectively, the sigma-tau Group) in January 2010. In addition to the initial sale of assets which has been reflected in the Company’s financial statements for the year ended December 31, 2010, there were certain potential future payments to Enzon that were contingent upon the achievement of stated milestones. During the first quarter of 2011, the Company earned a $5.0 million milestone payment resulting from the approval of a supplemental Biologic License Application (sBLA) for the manufacture of SS Oncaspar. Remaining potential milestone payments as of December 31, 2011 were estimated to be $17.0 million. In addition, there are royalties potentially due to Enzon of 5 to 10 percent on incremental net sales through 2014 by the sigma-tau Group above a 2009 baseline amount from the four marketed specialty pharmaceutical products Enzon sold to them. Approximately $0.5 million and $0.6 million of royalty revenue were recognized in 2011 and 2010, respectively, pursuant to this provision of the sale agreement. There can be no assurance that any of the remaining milestone payments or any future royalty revenues beyond that which has been recognized to date will accrue to the benefit of the Company. Also, the Company entered into a transition services agreement with sigma-tau Group whereby Enzon would perform product-support research and development for up to three years and provide various general and administrative functions for up to one year following the closing of the transaction. In consideration for this work, Enzon is being compensated based upon costs incurred plus a mark-up defined in the transition services agreement. Santaris Pharma A/S License Agreement In July 2006, the Company entered into a license agreement with Santaris Pharma A/S (Santaris) pursuant to which the Company obtained exclusive rights worldwide, other than in Europe, to develop and commercialize RNA antagonists directed against the HIF-1α and Survivin mRNA, as well as RNA antagonists directed against six additional gene targets selected by the Company. Since inception of the agreement, initial acquisition of in-process research and development and milestone payments have been made totaling $34.0 million, including milestone payments of $0.0 million, $7.0 million, and $3.0 million in 2011, 2010, and 2009, respectively, included in research and development expense in the accompanying statements of operations. The Company could pay an additional $142.0 million in milestone payments upon the successful completion of certain development and regulatory milestones. If the Company fails to make the requisite milestone payment for any particular target, Santaris has the right to recover that target for its own purposes. Santaris also is eligible to receive single-digit percentage royalties from any future product sales from products based on the licensed antagonists. Santaris retains the right to develop and commercialize products developed under the agreement in Europe. The royalty term expires on a country-by-country and product-by-product basis when the last valid LNA platform patent or LNA compound patent expires not to exceed 21 years with respect to any product. Merck Agreement As a result of a November 1990 agreement, the Company’s PEGylation technology was used to develop an improved version of the product INTRON A, PEGINTRON. Merck is responsible for marketing and manufacturing PEGINTRON on an exclusive worldwide basis and the Company receives royalties on worldwide sales of PEGINTRON for all indications. The Company has no involvement in the selling or marketing of PEGINTRON. Merck’s obligation to pay the Company royalties on sales of PEGINTRON terminates, on a country-by-country basis, upon the later of the date on which the last patent to contain a claim covering PEGINTRON expires in the country or 15 years after the first commercial sale of PEGINTRON in such country. Currently, expirations are expected to occur in 2016 in the U.S., 2018 in Europe and 2019 in Japan. The royalty percentage to which the Company is entitled will be lower in any country where a PEGylated alpha-interferon product is being marketed by a third party in competition with PEGINTRON where such third party is not Hoffmann-La Roche. Either party may terminate the agreement upon a material breach of the agreement by the other party that is not cured within 60 days of written notice from the non-breaching party or upon declaration of bankruptcy by the other party. During the quarter ended September 30, 2007, the Company sold a 25-percent interest in future royalties payable to it by Merck on net sales of PEGINTRON occurring after June 30, 2007. Nektar Agreement In January 2002, the Company entered into a PEGylation technology licensing agreement with Nektar under which the Company granted Nektar the right to grant sub-licenses for a portion of its patents related to its PEGylation technology to third-parties. Nektar had the right to sub-license Enzon’s patents that were defined in the January 2002 agreement and the Company will receive a royalty or a share of Nektar’s profits for any products that utilize the Company’s patented PEGylation technology. The Company’s receipt of royalties related to Nektar licenses will end in 2014. Effective in January 2007, Nektar’s right to grant additional sublicenses was limited to a certain class of our PEGylation technology. Existing sublicenses granted by Nektar prior to January 2007 were unaffected.

Significant Agreements

12 Months Ended

Dec. 31, 2011

Significant Agreements Disclosure [Text Block]

(18) Significant Agreements

Sigma-Tau Group

The Company sold its specialty pharmaceutical business to Klee Pharmaceuticals Inc. (now known as Sigma-Tau PharmaSource, Inc.), Defiante Farmacêutica, S.A and sigma-tau Finanziaria S.p.A. (collectively, the sigma-tau Group) in January 2010. In addition to the initial sale of assets which has been reflected in the Company’s financial statements for the year ended December 31, 2010, there were certain potential future payments to Enzon that were contingent upon the achievement of stated milestones. During the first quarter of 2011, the Company earned a $5.0 million milestone payment resulting from the approval of a supplemental Biologic License Application (sBLA) for the manufacture of SS Oncaspar. Remaining potential milestone payments as of December 31, 2011 were estimated to be $17.0 million. In addition, there are royalties potentially due to Enzon of 5 to 10 percent on incremental net sales through 2014 by the sigma-tau Group above a 2009 baseline amount from the four marketed specialty pharmaceutical products Enzon sold to them. Approximately $0.5 million and $0.6 million of royalty revenue were recognized in 2011 and 2010, respectively, pursuant to this provision of the sale agreement. There can be no assurance that any of the remaining milestone payments or any future royalty revenues beyond that which has been recognized to date will accrue to the benefit of the Company.

Also, the Company entered into a transition services agreement with sigma-tau Group whereby Enzon would perform product-support research and development for up to three years and provide various general and administrative functions for up to one year following the closing of the transaction. In consideration for this work, Enzon is being compensated based upon costs incurred plus a mark-up defined in the transition services agreement.

Santaris Pharma A/S License Agreement

In July 2006, the Company entered into a license agreement with Santaris Pharma A/S (Santaris) pursuant to which the Company obtained exclusive rights worldwide, other than in Europe, to develop and commercialize RNA antagonists directed against the HIF-1α and Survivin mRNA, as well as RNA antagonists directed against six additional gene targets selected by the Company. Since inception of the agreement, initial acquisition of in-process research and development and milestone payments have been made totaling $34.0 million, including milestone payments of $0.0 million, $7.0 million, and $3.0 million in 2011, 2010, and 2009, respectively, included in research and development expense in the accompanying statements of operations. The Company could pay an additional $142.0 million in milestone payments upon the successful completion of certain development and regulatory milestones. If the Company fails to make the requisite milestone payment for any particular target, Santaris has the right to recover that target for its own purposes. Santaris also is eligible to receive single-digit percentage royalties from any future product sales from products based on the licensed antagonists. Santaris retains the right to develop and commercialize products developed under the agreement in Europe. The royalty term expires on a country-by-country and product-by-product basis when the last valid LNA platform patent or LNA compound patent expires not to exceed 21 years with respect to any product.

Merck Agreement

As a result of a November 1990 agreement, the Company’s PEGylation technology was used to develop an improved version of the product INTRON A, PEGINTRON. Merck is responsible for marketing and manufacturing PEGINTRON on an exclusive worldwide basis and the Company receives royalties on worldwide sales of PEGINTRON for all indications. The Company has no involvement in the selling or marketing of PEGINTRON. Merck’s obligation to pay the Company royalties on sales of PEGINTRON terminates, on a country-by-country basis, upon the later of the date on which the last patent to contain a claim covering PEGINTRON expires in the country or 15 years after the first commercial sale of PEGINTRON in such country. Currently, expirations are expected to occur in 2016 in the U.S., 2018 in Europe and 2019 in Japan. The royalty percentage to which the Company is entitled will be lower in any country where a PEGylated alpha-interferon product is being marketed by a third party in competition with PEGINTRON where such third party is not Hoffmann-La Roche. Either party may terminate the agreement upon a material breach of the agreement by the other party that is not cured within 60 days of written notice from the non-breaching party or upon declaration of bankruptcy by the other party. During the quarter ended September 30, 2007, the Company sold a 25-percent interest in future royalties payable to it by Merck on net sales of PEGINTRON occurring after June 30, 2007.

Nektar Agreement

In January 2002, the Company entered into a PEGylation technology licensing agreement with Nektar under which the Company granted Nektar the right to grant sub-licenses for a portion of its patents related to its PEGylation technology to third-parties. Nektar had the right to sub-license Enzon’s patents that were defined in the January 2002 agreement and the Company will receive a royalty or a share of Nektar’s profits for any products that utilize the Company’s patented PEGylation technology. The Company’s receipt of royalties related to Nektar licenses will end in 2014. Effective in January 2007, Nektar’s right to grant additional sublicenses was limited to a certain class of our PEGylation technology. Existing sublicenses granted by Nektar prior to January 2007 were unaffected.