Summary of Significant Accounting Policies (Schedule of Revenue by Major Customers) (Details)	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Genentech [Member] | Avastin [Member]
Entity Wide Revenue Major Customer [Line Items]
Percentage of total revenue (in Percent)	33.00%		33.00%		34.00%		32.00%
Genentech [Member] | Herceptin [Member]
Entity Wide Revenue Major Customer [Line Items]
Percentage of total revenue (in Percent)	33.00%		35.00%		33.00%		35.00%
Genentech [Member] | Lucentis [Member]
Entity Wide Revenue Major Customer [Line Items]
Percentage of total revenue (in Percent)	21.00%		22.00%		18.00%		19.00%
Elan [Member] | Tysabri [Member]
Entity Wide Revenue Major Customer [Line Items]
Percentage of total revenue (in Percent)	9.00%	[1]	10.00%	[1]	11.00%	[1]	12.00%	[1]

[1] In April, 2013, Biogen Idec completed its purchase of Elan's interest in Tysabri. Prior to this our licensee for Tysabri was identified as Elan.