Assets and Liabilities Measured at Fair Value (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		12 Months Ended	134 Months Ended
	Mar. 31, 2013 item	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013	Dec. 31, 2011
Assets and Liabilities Measured at Fair Value
Transfer of assets from Level 1 to Level 2	$ 0			$ 0
Transfer of assets from Level 2 to Level 1	0			0
Proceeds from issuance of warrants	3,300,000
Number of inputs used in fair value classification	6
Warrants exercised (in shares)			0.5
Change in fair value of warrant liability	262,000	2,376,000		(1,291,000)
Weighted average assumptions used in the Black-Scholes valuation model for the warrants
Expected stock price volatility (as a percent)	98.80%	72.60%
Risk free interest rate (as a percent)	0.13%	0.31%
Expected life of warrants	11 months 1 day	1 year 11 months 1 day
Expected annual dividend per share (as a percent)	0.00%	0.00%
Assets:
Cash/Money market fund	26,736,000	24,523,000	33,971,000	26,736,000	25,668,000
Level 1
Assets:
Cash/Money market fund	26,376,000		33,971,000	26,376,000
Fair value of assets	26,736,000		33,971,000	26,736,000
Level 2
Assets:
Fair value of assets	58,015,000		65,151,000	58,015,000
Liabilities:
Secured debt	597,000		697,000	597,000
Fair value of liabilities	597,000		697,000	597,000
Level 2 | Corporate debt securities
Assets:
Fair value of assets	35,924,000		42,497,000	35,924,000
Level 2 | Commercial paper
Assets:
Fair value of assets	21,741,000		19,744,000	21,741,000
Level 2 | Certificate of deposit
Assets:
Fair value of assets	350,000		2,910,000	350,000
Level 3
Liabilities:
Warrant liability	1,170,000		908,000	1,170,000
Fair value of liabilities	1,170,000		908,000	1,170,000
Total
Assets:
Cash/Money market fund	26,376,000		33,971,000	26,376,000
Fair value of assets	84,751,000		99,122,000	84,751,000
Liabilities:
Secured debt	597,000		697,000	597,000
Warrant liability	1,170,000		908,000	1,170,000
Fair value of liabilities	1,767,000		1,605,000	1,767,000
Total | Corporate debt securities
Assets:
Fair value of assets	35,924,000		42,497,000	35,924,000
Total | Commercial paper
Assets:
Fair value of assets	21,741,000		19,744,000	21,741,000
Total | Certificate of deposit
Assets:
Fair value of assets	$ 350,000		$ 2,910,000	$ 350,000