Significant Contracts, Grants, License and Royalty Agreements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 Product	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 National Institute of Allergy and Infectious Diseases [Member]	Dec. 31, 2012 National Institute of Allergy and Infectious Diseases [Member]	Dec. 31, 2011 National Institute of Allergy and Infectious Diseases [Member]	Dec. 31, 2008 National Institute of Allergy and Infectious Diseases [Member]	Dec. 31, 2013 NIAID [Member]	Dec. 31, 2012 NIAID [Member]	Dec. 31, 2011 NIAID [Member]	Dec. 31, 2007 NIAID [Member]	Dec. 31, 2013 CytRx [Member]
Significant Contracts Grants License And Royalty Agreements [Line Items]
Number of licensed products Astellas agrees to develop	1
Paid for nonrefundable upfront license fee	$ 25.0
Milestone payment upon finalization of the trial design		10.0
Additional cash payments for achievement through commercial launch		95.0
Amount related to the license fee and know-how recognized by Company	0.7	10.7	25.3
Revenue related to contract services delivered	4.4	3.9	2.7
Revenue related to drug product delivered	1.2	1.8	0
Amount of grants awarded							2.0				6.0
Period of grant							2 years				3 years
Revenue recognized from grants				0	0	0.2		0	0	0.9
Extended period of grant				3 years				4 years
License fees	0.1	2.6	2.0									3.8
Percentage of certain initial upfront monetary payments to WARF	10.00%
Additional milestone payments related to in-license agreements	12.0
Payments related to the Company's independent programs	$ 7.7