Collaboration And License Agreements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended	1 Months Ended	12 Months Ended		6 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2009 years	Jan. 31, 2007 Genentech [Member]	Dec. 31, 2011 Millennium [Member]	Dec. 31, 2009 Millennium [Member]	Jun. 30, 2010 Product Collaboration Agreements [Member]	Nov. 30, 2009 Collaboration And Co-Development Agreement With Agensys [Member]	Dec. 31, 2011 Collaboration And Co-Development Agreement With Agensys [Member] months	Dec. 31, 2009 Millennium [Member]
Collaboration And License Agreements [Line Items]
Proceeds from upfront payment under collaboration		$ 60		$ 60		$ 12
Progress-dependent milestone payments		20	5
Deferred revenue					$ 70.0
Estimated development term and collaboration agreement, years	8
Estimated revenue recognition period, in months							78
Percentage of costs incurred development under collaboration								50.00%