STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) (USD $) In Thousands, except Share data, unless otherwise specified	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)	ACCUMULATED DEFICIT	Total
Balance at Dec. 31, 2009	$ 448	$ 379,621	$ 55	$ (368,589)	$ 11,535
Balance (in shares) at Dec. 31, 2009	44,772,945
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises and issuance of stock	1	283			284
Stock option exercises and issuance of stock (in shares)	43,621
Employee stock purchase plan	1	550			551
Employee stock purchase plan (in shares)	156,769
Stock based compensation expense		3,259			3,259
Change in unrealized gain (loss) on marketable securities			(62)		(62)
Net loss				(30,129)	(30,129)
Balance at Dec. 31, 2010	450	383,713	(7)	(398,718)	(14,562)
Balance (in shares) at Dec. 31, 2010	44,973,335
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from stock offering, net	80	46,676			46,756
Issuance of common stock from stock offering, net (in shares)	8,050,000
Stock option exercises and issuance of stock	7	3,935			3,942
Stock option exercises and issuance of stock (in shares)	692,916
Employee stock purchase plan	1	523			524
Employee stock purchase plan (in shares)	109,316
Stock based compensation expense		3,830			3,830
Change in unrealized gain (loss) on marketable securities			1		1
Net loss				(10,762)	(10,762)
Balance at Dec. 31, 2011	538	438,677	(6)	(409,480)	29,729
Balance (in shares) at Dec. 31, 2011	53,825,567				53,825,567
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from stock offering, net	82	56,174			56,256
Issuance of common stock from stock offering, net (in shares)	8,222,500
Stock option exercises and issuance of stock	3	1,347			1,350
Stock option exercises and issuance of stock (in shares)	254,893
Employee stock purchase plan	1	322			323
Employee stock purchase plan (in shares)	96,867
Stock based compensation expense		4,135			4,135
Change in unrealized gain (loss) on marketable securities			108		108
Net loss				(10,872)	(10,872)
Balance at Dec. 31, 2012	$ 624	$ 500,655	$ 102	$ (420,352)	$ 81,029
Balance (in shares) at Dec. 31, 2012	62,399,827				62,399,827