Legal Matters	12 Months Ended
Dec. 31, 2012
Commitments and Contingencies Disclosure [Abstract]
Legal Matters	Legal Matters From time to time, the Company is a party to legal proceedings in the course of the Company’s business. The Company does not expect any such current ordinary course legal proceedings to have a material adverse effect on the Company’s business or financial condition. Costs associated with the Company’s involvement in legal proceedings are expensed as incurred. Genentech Patent Litigation The Company is aware of issued patents and pending patent applications owned by Genentech that claim certain chimeric VEGF receptors. The Company does not believe that ZALTRAP or EYLEA infringe any valid claim in these patents or patent applications. The Company is involved in five patent litigations with Genentech, two in the United States and three in Europe. In November 2010, the Company commenced a lawsuit against Genentech in the U.S. District Court for the Southern District of New York (the "Court"), seeking a declaratory judgment that no activities relating to the Company's VEGF Trap infringe any valid claim of certain Genentech patents referred to as the Davis-Smyth patents (the "First Davis-Smyth Case"). Genentech answered the complaint and asserted counterclaims that the Company's prior or planned activities relating to VEGF Trap have infringed or will infringe claims of four of the Davis-Smyth patents and requested a judgment against the Company for damages, including for willful infringement, and other relief as the Court deems appropriate. On December 31, 2011, the Company entered into a Non-Exclusive License and Partial Settlement Agreement with Genentech (the "Genentech Agreement") that covers making, using, and selling EYLEA in the United States for the prevention and treatment of human eye diseases and disorders in the United States, and ends the litigation relating to those matters. Under the Genentech Agreement, the Company received a non-exclusive license to the Davis-Smyth patents, and certain other technology patents owned or co-owned by Genentech. The Genentech Agreement does not cover any non-U.S. patent rights or non-U.S. patent disputes, and does not cover any use of aflibercept other than for prevention and treatment of human eye diseases and disorders in the United States. The First Davis-Smyth Case is continuing with respect to matters not covered by the Genentech Agreement. The Genentech Agreement provides for the Company to make payments to Genentech based on U.S. sales of EYLEA through May 7, 2016, the date the Davis-Smyth patents expire. As required by the Genentech Agreement, in 2012, the Company made a lump-sum payment of $60.0 million when cumulative U.S. sales of EYLEA reached $400 million. The Company will also pay royalties of 4.75% on cumulative U.S. sales of EYLEA between $400 million and $3 billion and 5.5% on any cumulative U.S. sales of EYLEA over $3 billion. As a result of the Genentech Agreement, on January 17, 2012, Genentech filed a second amended answer and counterclaim in the First Davis-Smyth Case, in which it amended its counterclaims alleging infringement of four of the Davis-Smyth patents. On December 23, 2011, Genentech initiated a related case in the Court against Regeneron and Sanofi alleging infringement of four of the Davis-Smyth Patents by activities relating to VEGF Trap (but excluding EYLEA) (the "Second Davis-Smyth Case"). As in the First Davis-Smyth Case, in the new complaint Genentech requests a judgment against the Company for damages, including for willful infringement, and other relief as the Court deems appropriate. On September 21, 2012, Genentech asserted two additional Davis-Smyth patents, and one additional application (which was allowed and issued as a patent on September 25, 2012) in both the First David-Smyth Case and the Second Davis-Smyth Case. The Company believes Genentech's remaining claims in the First Davis Smyth Case and the Second Davis Smyth Case are without merit and intends to continue to defend against all of Genentech's remaining claims vigorously. As this litigation is at an early stage, at this time the Company is not able to predict the probability of the outcome or an estimate of loss, if any, related to these matters. The Company has initiated patent-related actions against Genentech in Germany, the United Kingdom, and Italy relating in each case to a patent that expired on October 28, 2012. The Company may initiate other actions in other countries outside the United States, which could have similar or other adverse outcomes that would materially harm its business and which, irrespective of the outcomes, may also entail significant costs and expenses. In the United Kingdom, an adverse decision dated March 22, 2012 is under appeal. This decision found the designation of European patent EP 1 238 986 in the United Kingdom to be valid and potential acts relating to VEGF Trap-Eye in the United Kingdom before expiration of the patent on October 28, 2012 to infringe this patent.

Legal Matters

From time to time, the Company is a party to legal proceedings in the course of the Company’s business. The Company does not expect any such current ordinary course legal proceedings to have a material adverse effect on the Company’s business or financial condition. Costs associated with the Company’s involvement in legal proceedings are expensed as incurred.

Genentech Patent Litigation

The Company is aware of issued patents and pending patent applications owned by Genentech that claim certain chimeric VEGF receptors. The Company does not believe that ZALTRAP or EYLEA infringe any valid claim in these patents or patent applications. The Company is involved in five patent litigations with Genentech, two in the United States and three in Europe. In November 2010, the Company commenced a lawsuit against Genentech in the U.S. District Court for the Southern District of New York (the "Court"), seeking a declaratory judgment that no activities relating to the Company's VEGF Trap infringe any valid claim of certain Genentech patents referred to as the Davis-Smyth patents (the "First Davis-Smyth Case"). Genentech answered the complaint and asserted counterclaims that the Company's prior or planned activities relating to VEGF Trap have infringed or will infringe claims of four of the Davis-Smyth patents and requested a judgment against the Company for damages, including for willful infringement, and other relief as the Court deems appropriate.

On December 31, 2011, the Company entered into a Non-Exclusive License and Partial Settlement Agreement with Genentech (the "Genentech Agreement") that covers making, using, and selling EYLEA in the United States for the prevention and treatment of human eye diseases and disorders in the United States, and ends the litigation relating to those matters. Under the Genentech Agreement, the Company received a non-exclusive license to the Davis-Smyth patents, and certain other technology patents owned or co-owned by Genentech. The Genentech Agreement does not cover any non-U.S. patent rights or non-U.S. patent disputes, and does not cover any use of aflibercept other than for prevention and treatment of human eye diseases and disorders in the United States. The First Davis-Smyth Case is continuing with respect to matters not covered by the Genentech Agreement. The Genentech Agreement provides for the Company to make payments to Genentech based on U.S. sales of EYLEA through May 7, 2016, the date the Davis-Smyth patents expire. As required by the Genentech Agreement, in 2012, the Company made a lump-sum payment of $60.0 million when cumulative U.S. sales of EYLEA reached $400 million. The Company will also pay royalties of 4.75% on cumulative U.S. sales of EYLEA between $400 million and $3 billion and 5.5% on any cumulative U.S. sales of EYLEA over $3 billion. As a result of the Genentech Agreement, on January 17, 2012, Genentech filed a second amended answer and counterclaim in the First Davis-Smyth Case, in which it amended its counterclaims alleging infringement of four of the Davis-Smyth patents. On December 23, 2011, Genentech initiated a related case in the Court against Regeneron and Sanofi alleging infringement of four of the Davis-Smyth Patents by activities relating to VEGF Trap (but excluding EYLEA) (the "Second Davis-Smyth Case"). As in the First Davis-Smyth Case, in the new complaint Genentech requests a judgment against the Company for damages, including for willful infringement, and other relief as the Court deems appropriate. On September 21, 2012, Genentech asserted two additional Davis-Smyth patents, and one additional application (which was allowed and issued as a patent on September 25, 2012) in both the First David-Smyth Case and the Second Davis-Smyth Case.

The Company believes Genentech's remaining claims in the First Davis Smyth Case and the Second Davis Smyth Case are without merit and intends to continue to defend against all of Genentech's remaining claims vigorously. As this litigation is at an early stage, at this time the Company is not able to predict the probability of the outcome or an estimate of loss, if any, related to these matters.

The Company has initiated patent-related actions against Genentech in Germany, the United Kingdom, and Italy relating in each case to a patent that expired on October 28, 2012. The Company may initiate other actions in other countries outside the United States, which could have similar or other adverse outcomes that would materially harm its business and which, irrespective of the outcomes, may also entail significant costs and expenses. In the United Kingdom, an adverse decision dated March 22, 2012 is under appeal. This decision found the designation of European patent EP 1 238 986 in the United Kingdom to be valid and potential acts relating to VEGF Trap-Eye in the United Kingdom before expiration of the patent on October 28, 2012 to infringe this patent.