Acquisitions	3 Months Ended
Mar. 31, 2018
Business Combinations [Abstract]
Acquisitions	Acquisitions Karyopharm Therapeutics Inc. In January 2018 we acquired the exclusive worldwide rights to develop and commercialize Karyopharm Therapeutics Inc.'s (Karyopharm) Phase 1 ready investigational oral compound BIIB100 (formerly known as KPT-350) for the treatment of certain neurological and neurodegenerative conditions, primarily in ALS. BIIB100 is a novel therapeutic candidate that works by inhibiting a protein known as XPO1, with the goal of reducing inflammation and neurotoxicity, along with increasing neuroprotective responses. We accounted for this transaction as an asset acquisition as the value being acquired relates to a single asset. In connection with the closing of this transaction, we made an upfront payment of $10.0 million, which was recorded as acquired in-process research and development in our condensed consolidated statements of income as BIIB100 has not yet reached technological feasibility. We have also agreed to pay Karyopharm up to $207.0 million in additional milestone payments, as well as potential royalties.

Acquisitions

Karyopharm Therapeutics Inc.

In January 2018 we acquired the exclusive worldwide rights to develop and commercialize Karyopharm Therapeutics Inc.'s (Karyopharm) Phase 1 ready investigational oral compound BIIB100 (formerly known as KPT-350) for the treatment of certain neurological and neurodegenerative conditions, primarily in ALS. BIIB100 is a novel therapeutic candidate that works by inhibiting a protein known as XPO1, with the goal of reducing inflammation and neurotoxicity, along with increasing neuroprotective responses.

We accounted for this transaction as an asset acquisition as the value being acquired relates to a single asset. In connection with the closing of this transaction, we made an upfront payment of $10.0 million, which was recorded as acquired in-process research and development in our condensed consolidated statements of income as BIIB100 has not yet reached technological feasibility. We have also agreed to pay Karyopharm up to $207.0 million in additional milestone payments, as well as potential royalties.