Assets and Liabilities Measured at Fair Value (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended	137 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 item	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013	Dec. 31, 2011
Assets and Liabilities Measured at Fair Value
Transfer of assets from Level 1 to Level 2	$ 0		$ 0			$ 0
Transfer of assets from Level 2 to Level 1	0		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	(619,000)	118,000	(357,000)	2,494,000		(1,910,000)
Weighted average assumptions used in the Black-Scholes valuation model for the warrants
Expected stock price volatility (as a percent)			111.44%	73.27%
Risk free interest rate (as a percent)			0.11%	0.29%
Expected life of warrants			8 months 1 day	1 year 8 months 1 day
Expected annual dividend per share (as a percent)			0.00%	0.00%
Assets:
Cash/Money market fund	23,476,000	28,858,000	23,476,000	28,858,000	33,971,000	23,476,000	25,668,000
Level 1
Assets:
Cash/Money market fund	23,476,000		23,476,000		33,971,000	23,476,000
Fair value of assets	23,476,000		23,476,000		33,971,000	23,476,000
Level 2
Assets:
Fair value of assets	50,700,000		50,700,000		65,151,000	50,700,000
Liabilities:
Secured debt	498,000		498,000		697,000	498,000
Fair value of liabilities	498,000		498,000		697,000	498,000
Level 2 | Corporate debt securities
Assets:
Fair value of assets	29,604,000		29,604,000		42,497,000	29,604,000
Level 2 | Commercial paper
Assets:
Fair value of assets	20,746,000		20,746,000		19,744,000	20,746,000
Level 2 | Certificate of deposit
Assets:
Fair value of assets	350,000		350,000		2,910,000	350,000
Level 3
Liabilities:
Warrant liability	551,000		551,000		908,000	551,000
Fair value of liabilities	551,000		551,000		908,000	551,000
Increase/(Decrease) in fair value	(600,000)	(100,000)	(400,000)	(2,500,000)
Total
Assets:
Cash/Money market fund	23,476,000		23,476,000		33,971,000	23,476,000
Fair value of assets	74,176,000		74,176,000		99,122,000	74,176,000
Liabilities:
Secured debt	498,000		498,000		697,000	498,000
Warrant liability	551,000		551,000		908,000	551,000
Fair value of liabilities	1,049,000		1,049,000		1,605,000	1,049,000
Total | Corporate debt securities
Assets:
Fair value of assets	29,604,000		29,604,000		42,497,000	29,604,000
Total | Commercial paper
Assets:
Fair value of assets	20,746,000		20,746,000		19,744,000	20,746,000
Total | Certificate of deposit
Assets:
Fair value of assets	$ 350,000		$ 350,000		$ 2,910,000	$ 350,000