Gain on Sale of Rights (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gain on Sale of Rights [Abstract]
Gain on sale of rights	$ 16,758biib_GainOnSaleOfRights	$ 24,898biib_GainOnSaleOfRights	$ 46,792biib_GainOnSaleOfRights

Gain on sale of our royalty and other rights related to future sales of BENLYSTA recognized in our consolidated statement of income.

No definition available.