Subsequent Events Subsequent Events	6 Months Ended
Jun. 30, 2015
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Applied Genetic Technologies Corporation On July 2, 2015, we announced a collaboration and license agreement to develop gene-based therapies for multiple ophthalmic diseases with Applied Genetic Technologies Corporation (AGTC). The collaboration will focus on the development of a portfolio of AGTC’s therapeutic programs, including both a clinical stage candidate for X-linked Retinoschisis (XLRS) and a pre-clinical candidate for the treatment of X-Linked Retinitis Pigmentosa (XLRP). The agreement also includes options for early stage discovery programs in two ophthalmic diseases and one non-ophthalmic condition, as well as an equity investment in AGTC by Biogen and a license agreement for manufacturing rights. Upon closing, we will make an upfront payment in the amount of $124.0 million to AGTC, which includes a $30.0 million equity investment in AGTC, prepaid research and development expenditures of $58.4 million and total licensing and other fees of $35.6 million. We will be granted a license to the XLRS and XLRP programs and the option to license discovery programs for three additional indications at the time of clinical candidate selection. Under the collaboration, AGTC is eligible to receive upfront and milestone payments aggregating in excess of $1.0 billion. This includes up to $472.5 million collectively for the two lead programs, which also will carry royalties in the high single digit to mid-teen percentages of annual net sales. In addition, we will make payments up to $592.5 million across the discovery programs, along with royalties in the mid-single digits to low-teen percentages of annual net sales. We will be granted worldwide commercialization rights for the XLRS and XLRP programs. AGTC has an option to share development costs and profits after the initial clinical trial data are available, and an option to co-promote the second of these products to be approved in the U.S. AGTC will lead the clinical development programs of XLRS through product approval and of XLRP through the completion of first-in-human trials. We will support the clinical development costs, subject to certain conditions, following the first-in-human study for XLRS and IND-enabling studies for XLRP. Under the manufacturing license, we will receive an exclusive license to use AGTC’s proprietary technology platform to make AAV vectors for up to six genes, three of which are in AGTC’s discretion, in exchange for payment of milestones and royalties. The transaction is subject to customary closing conditions, including the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 in the U.S., and is expected to close in the third quarter of 2015. Research Triangle Park Facility Purchase On July 15, 2015, we entered into an arrangement with Eisai, Inc. (Eisai) to purchase their manufacturing facility in Research Triangle Park, North Carolina, including a drug product facility and supporting infrastructure. Currently, we are leasing a portion of this facility in order to manufacture our and Eisai's oral solid dose products under a 10 year lease. We have committed to buy that portion of the facility upon Eisai’s completion of certain transition activities. The transaction is subject to customary closing conditions, including the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 in the U.S., and is expected to close in the third quarter of 2015. Swedish Orphan Biovitrum AB On July 16, 2015, Swedish Orphan Biovitrum AB (Sobi) exercised its option to assume development and commercialization of ALPROLIX in Europe, Russia, Turkey and certain markets in the Middle East and paid us $10.0 million, which will be held in escrow pending E.U. regulatory approval. We collaborate with Sobi to jointly develop and commercialize Factor VIII and Factor IX hemophilia products, including ELOCTATE and ALPROLIX. For more information about our agreement with Sobi, please read Note 20, Collaborative and Other Relationships to our consolidated financial statements included within our 2014 Form 10-K.

Subsequent Events

Applied Genetic Technologies Corporation

On July 2, 2015, we announced a collaboration and license agreement to develop gene-based therapies for multiple ophthalmic diseases with Applied Genetic Technologies Corporation (AGTC). The collaboration will focus on the development of a portfolio of AGTC’s therapeutic programs, including both a clinical stage candidate for X-linked Retinoschisis (XLRS) and a pre-clinical candidate for the treatment of X-Linked Retinitis Pigmentosa (XLRP). The agreement also includes options for early stage discovery programs in two ophthalmic diseases and one non-ophthalmic condition, as well as an equity investment in AGTC by Biogen and a license agreement for manufacturing rights.

Upon closing, we will make an upfront payment in the amount of $124.0 million to AGTC, which includes a $30.0 million equity investment in AGTC, prepaid research and development expenditures of $58.4 million and total licensing and other fees of $35.6 million. We will be granted a license to the XLRS and XLRP programs and the option to license discovery programs for three additional indications at the time of clinical candidate selection.

Under the collaboration, AGTC is eligible to receive upfront and milestone payments aggregating in excess of $1.0 billion. This includes up to $472.5 million collectively for the two lead programs, which also will carry royalties in the high single digit to mid-teen percentages of annual net sales. In addition, we will make payments up to $592.5 million across the discovery programs, along with royalties in the mid-single digits to low-teen percentages of annual net sales.

We will be granted worldwide commercialization rights for the XLRS and XLRP programs. AGTC has an option to share development costs and profits after the initial clinical trial data are available, and an option to co-promote the second of these products to be approved in the U.S. AGTC will lead the clinical development programs of XLRS through product approval and of XLRP through the completion of first-in-human trials. We will support the clinical development costs, subject to certain conditions, following the first-in-human study for XLRS and IND-enabling studies for XLRP. Under the manufacturing license, we will receive an exclusive license to use AGTC’s proprietary technology platform to make AAV vectors for up to six genes, three of which are in AGTC’s discretion, in exchange for payment of milestones and royalties.

The transaction is subject to customary closing conditions, including the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 in the U.S., and is expected to close in the third quarter of 2015.

Research Triangle Park Facility Purchase

On July 15, 2015, we entered into an arrangement with Eisai, Inc. (Eisai) to purchase their manufacturing facility in Research Triangle Park, North Carolina, including a drug product facility and supporting infrastructure.

Currently, we are leasing a portion of this facility in order to manufacture our and Eisai's oral solid dose products under a 10 year lease. We have committed to buy that portion of the facility upon Eisai’s completion of certain transition activities.

Swedish Orphan Biovitrum AB

On July 16, 2015, Swedish Orphan Biovitrum AB (Sobi) exercised its option to assume development and commercialization of ALPROLIX in Europe, Russia, Turkey and certain markets in the Middle East and paid us $10.0 million, which will be held in escrow pending E.U. regulatory approval.

We collaborate with Sobi to jointly develop and commercialize Factor VIII and Factor IX hemophilia products, including ELOCTATE and ALPROLIX. For more information about our agreement with Sobi, please read Note 20, Collaborative and Other Relationships to our consolidated financial statements included within our 2014 Form 10-K.