Condensed Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 48,491	$ 26,278
Short-term investments	9,789	3,125
Prepaid expenses and other current assets	1,102	874
Total current assets	59,382	30,277
Long-term investments		6,189
Property and equipment, net	926	90
Restricted cash and other assets	324	311
Total assets	60,632	36,867
Current liabilities:
Accounts payable	2,064	904
Accrued expenses	4,616	3,506
Current portion of note payable	59
Total current liabilities	6,739	4,410
Note payable, net of current portion	804
Other liabilities	268	5
Total liabilities	7,811	4,415
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.01 par value, Authorized - 5,000 shares	0	0
Common stock, $0.001 par value, Authorized - 280,000 shares; Issued and outstanding - 85,802 and 66,252 shares at September 30, 2014 and December 31, 2013, respectively	86	66
Additional paid-in capital	486,817	434,285
Accumulated deficit	(439,608)	(412,884)
Accumulated other comprehensive loss	(2)	(7)
Total stockholders' equity	52,821	32,452
Total liabilities and stockholders' equity	60,632	36,867
Series E preferred stock [Member]
Stockholders' equity:
Preferred stock, $0.01 par value	5,528	5,528
Series D preferred stock [Member]
Stockholders' equity:
Preferred stock, $0.01 par value		5,464
Series A preferred stock [Member]
Stockholders' equity:
Preferred stock, $0.01 par value	$ 0	$ 0