Significant Accounting Policies (Details) (USD $)	3 Months Ended								12 Months Ended			163 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Financial Instruments
Fair value and carrying value of notes payable and capital lease obligations	$ 1,400,000				$ 7,200,000				$ 1,400,000	$ 7,200,000		$ 1,400,000
Cash and Cash Equivalents
Cash and cash equivalents	20,250,000				39,490,000				20,250,000	39,490,000		20,250,000
Leasehold Improvements and Equipment
Tenant improvement allowance									622,000
Deferred rents	1,500,000				913,000				1,500,000	913,000		1,500,000
Revenue Recognition
Grant revenue	299,000	327,000	590,000	471,000	301,000	430,000	537,000	604,000	1,687,000	1,872,000	2,079,000	7,404,000
Research and Development
Iowa refundable research credit									$ 283,000	$ 160,000	$ 230,000	$ 2,100,000
Stock Option Valuation
ISO Stockholder Ownership Threshold									10.00%
Greater Than 10% Stockholder ISO Exercise Price Threshold									110.00%
Greater Than 10% Stockholder ISO Term									5