VIIV Healthcare Company and Glaxosmithkline Collaboration (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
	Mar. 31, 2012	Sep. 30, 2012
ViiV Healthcare Company and Glaxosmithkline Collaboration (Textual) [Abstract]
Recognized deferred collaboration revenue	$ 36.1
ViiV Healthcare Company and Glaxosmithkline Collaboration [Member]
ViiV Healthcare Company and Glaxosmithkline Collaboration (Textual) [Abstract]
Net amount received related to collaboration		34.0
Recognized deferred collaboration revenue	36.1
GSK stock purchase agreement [Member]
ViiV Healthcare Company and Glaxosmithkline Collaboration (Textual) [Abstract]
Common stock purchased under collaboration agreement		2.5
Aggregate purchase price of common stock under collaboration agreement		17.0
Purchase price of common stock under collaboration agreement, per share		$ 6.87
Effective date of GSK stock purchase agreement		March 2009
GSK stock purchase agreement [Member] | Achievement of preclinical operational milestone [Member]
ViiV Healthcare Company and Glaxosmithkline Collaboration (Textual) [Abstract]
Milestone payment received related to ViiV license agreement		6.5
ViiV license agreement [Member]
ViiV Healthcare Company and Glaxosmithkline Collaboration (Textual) [Abstract]
Milestone payment received related to ViiV license agreement		17.0
Potential additional maximum milestone payments received related to ViiV license agreement		390.0
License agreement, life		17 years
ViiV license agreement, terminated date		March 15, 2012
ViiV license agreement [Member] | Initiation of phase IIb clinical study of '761 [Member]
ViiV Healthcare Company and Glaxosmithkline Collaboration (Textual) [Abstract]
Milestone payment received related to ViiV license agreement		$ 20.0