Condensed Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 54,886	$ 26,278
Short-term investments	8,844	3,125
Prepaid expenses and other current assets	836	874
Total current assets	64,566	30,277
Long-term investments	1,004	6,189
Property and equipment, net	686	90
Restricted cash	311	311
Total assets	66,567	36,867
Current liabilities:
Accounts payable	2,026	904
Accrued expenses	4,221	3,506
Total current liabilities	6,247	4,410
Other liabilities	59	5
Total liabilities	6,306	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 - 83,758 and 66,252 shares at June 30, 2014 and December 31, 2013, respectively	84	66
Additional paid-in capital	484,799	434,285
Accumulated deficit	(430,153)	(412,884)
Accumulated other comprehensive gain (loss)	3	(7)
Total stockholders' equity	60,261	32,452
Total liabilities and stockholders' equity	66,567	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