Acquisitions	9 Months Ended
Sep. 30, 2017
Business Combinations [Abstract]
Acquisitions	Acquisitions On May 15, 2017, we completed an asset purchase of the Phase 3 candidate, CIRARA (now known as BIIB093), from Remedy Pharmaceuticals Inc. (Remedy). The target indication for BIIB093 is large hemispheric infarction (LHI), a severe form of ischemic stroke where brain swelling (cerebral edema) often leads to a disproportionately large share of stroke-related morbidity and mortality. The U.S. Food and Drug Administration (FDA) recently granted BIIB093 Orphan Drug designation for severe cerebral edema in patients with acute ischemic stroke. The FDA has also granted BIIB093 Fast Track designation. Under the terms of the purchase agreement, we will have responsibility for the future development and commercialization of BIIB093 and have agreed to pay Remedy certain development and sales based milestone payments, which are substantially payable upon or after regulatory approval, as well as royalties on future commercial sales. Remedy will share in the cost of development for the target indication for BIIB093 in LHI stroke. We accounted for this transaction as an asset acquisition as we did not acquire any employees from Remedy nor did we acquire any significant processes required in the development of BIIB093. Upon closing of the transaction, we made a $120.0 million upfront payment, which was recorded as acquired in-process research and development in our condensed consolidated statements of income as BIIB093 has not yet reached technological feasibility.

Acquisitions

On May 15, 2017, we completed an asset purchase of the Phase 3 candidate, CIRARA (now known as BIIB093), from Remedy Pharmaceuticals Inc. (Remedy). The target indication for BIIB093 is large hemispheric infarction (LHI), a severe form of ischemic stroke where brain swelling (cerebral edema) often leads to a disproportionately large share of stroke-related morbidity and mortality. The U.S. Food and Drug Administration (FDA) recently granted BIIB093 Orphan Drug designation for severe cerebral edema in patients with acute ischemic stroke. The FDA has also granted BIIB093 Fast Track designation. Under the terms of the purchase agreement, we will have responsibility for the future development and commercialization of BIIB093 and have agreed to pay Remedy certain development and sales based milestone payments, which are substantially payable upon or after regulatory approval, as well as royalties on future commercial sales. Remedy will share in the cost of development for the target indication for BIIB093 in LHI stroke.

We accounted for this transaction as an asset acquisition as we did not acquire any employees from Remedy nor did we acquire any significant processes required in the development of BIIB093. Upon closing of the transaction, we made a $120.0 million upfront payment, which was recorded as acquired in-process research and development in our condensed consolidated statements of income as BIIB093 has not yet reached technological feasibility.