Subsequent events (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jul. 08, 2011	Dec. 31, 2010
Statement of Financial Position [Abstract]
Stock issued, underwritten public offering, value		$ 20,400,000
Stock issued underwritten public offering (in shares)		5,600,000
Warrants per share value (in dollars per share)		$ 0.07
Net proceeds from the issuance of common shares	0	18,900,000	18,943,119
Common stock, shares outstanding (in shares)	21,307,916	21,294,413
Current assets:
Cash and cash equivalents	12,453,637	17,988,590	30,387,583		6,324,430
Short-term investments	10,000,000	18,057,672
Prepaid and other current assets	1,200,084	1,017,799
Total current assets	23,762,225	37,281,040
Total assets	24,358,790	37,854,423
LIABILITIES AND STOCKHOLDERS' EQUITY
Total current liabilities	20,601,016	13,600,353
Stockholders' equity [Abstract]
Common stock	21,308	21,294
Additional paid-in-capital	238,769,155	237,452,308
Treasury stock	2,279,238	2,279,238
Accumulated deficit	(232,753,451)	(210,940,294)
Total stockholders' equity	3,757,774	24,254,070
Total liabilities and stockholders' equity	24,358,790	37,854,423
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, shares authorized (in shares)	5,000,000	5,000,000
Series A Junior Participating Preferred Stock, shares authorized (in shares)	25,000	25,000		15,000
Preferred Stock, shares outstanding (in shares)	0	0
Preferred Stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	250,000,000	250,000,000		175,000,000
Common stock, shares issued (in shares)	21,307,916	21,294,413
Treasury stock (in shares)	90,546	90,546
Actual [Member]
Current assets:
Cash and cash equivalents	12,453,637
Short-term investments	10,000,000
Prepaid and other current assets	1,308,588
Total current assets	23,762,225
Non-current assets	596,565
Total assets	24,358,790
LIABILITIES AND STOCKHOLDERS' EQUITY
Total current liabilities	20,601,016
Stockholders' equity [Abstract]
Common stock	21,308
Additional paid-in-capital	238,769,155
Treasury stock	(2,279,238)
Accumulated deficit	(232,753,451)
Total stockholders' equity	3,757,774
Total liabilities and stockholders' equity	24,358,790
Adjustment [Member]
Current assets:
Cash and cash equivalents	21,400,000
Short-term investments	0
Prepaid and other current assets	0
Total current assets	21,400,000
Non-current assets	0
Total assets	21,400,000
Stockholders' equity [Abstract]
Common stock	9,200
Additional paid-in-capital	21,390,800
Treasury stock	0
Accumulated deficit	0
Total stockholders' equity	21,400,000
Total liabilities and stockholders' equity	21,400,000
Pro Forma [Member]
Current assets:
Cash and cash equivalents	33,853,637
Short-term investments	10,000,000
Prepaid and other current assets	1,308,588
Total current assets	45,162,225
Non-current assets	596,565
Total assets	45,758,790
LIABILITIES AND STOCKHOLDERS' EQUITY
Total current liabilities	20,601,016
Stockholders' equity [Abstract]
Common stock	30,508
Additional paid-in-capital	260,159,955
Treasury stock	(2,279,238)
Accumulated deficit	(232,753,451)
Total stockholders' equity	25,157,774
Total liabilities and stockholders' equity	45,758,790
Subsequent Event [Member]
Statement of Financial Position [Abstract]
Stock issued, underwritten public offering, value	23,000,000
Stock issued underwritten public offering (in shares)	9,200,000
Warrants per share value (in dollars per share)	$ 2.50
Net proceeds from the issuance of common shares	$ 21,400,000
Common stock, shares outstanding (in shares)	30.5