Legal Matters (Notes)	9 Months Ended
Sep. 30, 2014
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. Costs associated with the Company's involvement in legal proceedings are expensed as incurred. Proceedings Relating to ‘287 Patent and '018 Patent The Company is a party to patent infringement litigation involving its European Patent No. 1,360,287 (the "'287 Patent") and its U.S. Patent No. 8,502,018 (the "'018 Patent"), both of which concern genetically altered mice capable of producing chimeric antibodies that are part human and part mouse. Chimeric antibody sequences can be used to produce high-affinity fully human monoclonal antibodies. In these proceedings (the "'287 Patent Infringement Litigation" and "'018 Patent Infringement Litigation," respectively), the Company claims infringement of several claims of the '287 Patent and the '018 Patent (as applicable), and seeks, among other types of relief, an injunction and an account of profits in connection with the defendants' infringing acts, which may include, among other things, the making, use, keeping, sale, or offer for sale of genetically engineered mice (or certain cells from which they are derived) that infringe one or more claims of the '287 Patent and the '018 Patent (as applicable). With respect to the '018 Patent Infringement Litigation against Ablexis, LLC, on October 31, 2014, the Company and Ablexis reached a confidential settlement and filed a joint stipulation dismissing the action with prejudice. As the '287 Patent Infringement Litigation and remaining '018 Patent Infringement Litigation proceedings are at an early stage, at this time the Company is not able to predict the outcome of, or an estimate of gain, if any, related to, these proceedings. Proceedings Relating to PCSK9 Antibody (Alirocumab) On October 17, 2014 and October 28, 2014, Amgen Inc. filed lawsuits against Regeneron, Sanofi, Aventisub LLC, and Aventis Pharmaceuticals, Inc. in the United States District Court for the District of Delaware seeking an injunction to prevent Regeneron and the other defendants from making, using, offering to sell, or selling within the United States (as well as importing into the United States) alirocumab, the antibody to PCSK9 for LDL cholesterol reduction Regeneron is jointly developing with Sanofi. In the complaints, Amgen asserts U.S. Patent Nos. 8,563,698, 8,829,165, and 8,859,741 and U.S. Patent Nos. 8,871,913 and 8,871,914, respectively. Amgen also seeks a judgment of patent infringement of the asserted patents, monetary damages (together with interest), costs and expenses of the lawsuits, and attorneys’ fees. This matter has not yet progressed sufficiently through discovery and/or development of important factual information and legal issues to enable the Company to estimate a range of possible loss, if any.

Legal Matters

From time to time, the Company is a party to legal proceedings in the course of the Company's business. Costs associated with the Company's involvement in legal proceedings are expensed as incurred.

Proceedings Relating to ‘287 Patent and '018 Patent

The Company is a party to patent infringement litigation involving its European Patent No. 1,360,287 (the "'287 Patent") and its U.S. Patent No. 8,502,018 (the "'018 Patent"), both of which concern genetically altered mice capable of producing chimeric antibodies that are part human and part mouse. Chimeric antibody sequences can be used to produce high-affinity fully human monoclonal antibodies. In these proceedings (the "'287 Patent Infringement Litigation" and "'018 Patent Infringement Litigation," respectively), the Company claims infringement of several claims of the '287 Patent and the '018 Patent (as applicable), and seeks, among other types of relief, an injunction and an account of profits in connection with the defendants' infringing acts, which may include, among other things, the making, use, keeping, sale, or offer for sale of genetically engineered mice (or certain cells from which they are derived) that infringe one or more claims of the '287 Patent and the '018 Patent (as applicable). With respect to the '018 Patent Infringement Litigation against Ablexis, LLC, on October 31, 2014, the Company and Ablexis reached a confidential settlement and filed a joint stipulation dismissing the action with prejudice. As the '287 Patent Infringement Litigation and remaining '018 Patent Infringement Litigation proceedings are at an early stage, at this time the Company is not able to predict the outcome of, or an estimate of gain, if any, related to, these proceedings.

Proceedings Relating to PCSK9 Antibody (Alirocumab)

On October 17, 2014 and October 28, 2014, Amgen Inc. filed lawsuits against Regeneron, Sanofi, Aventisub LLC, and Aventis Pharmaceuticals, Inc. in the United States District Court for the District of Delaware seeking an injunction to prevent Regeneron and the other defendants from making, using, offering to sell, or selling within the United States (as well as importing into the United States) alirocumab, the antibody to PCSK9 for LDL cholesterol reduction Regeneron is jointly developing with Sanofi. In the complaints, Amgen asserts U.S. Patent Nos. 8,563,698, 8,829,165, and 8,859,741 and U.S. Patent Nos. 8,871,913 and 8,871,914, respectively. Amgen also seeks a judgment of patent infringement of the asserted patents, monetary damages (together with interest), costs and expenses of the lawsuits, and attorneys’ fees. This matter has not yet progressed sufficiently through discovery and/or development of important factual information and legal issues to enable the Company to estimate a range of possible loss, if any.