BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 14,327	$ 11,095
Marketable securities-short term	64,944	57,073
Prepaid expenses and other current assets	344	4,020
Total current assets	79,615	72,188
Marketable securities-long term	51,328	40,475
Property and equipment, net	1,992	2,939
Other assets	1,258	1,449
Total assets	134,193	117,051
Current liabilities:
Accounts payable and accrued expenses	10,163	11,932
Notes payable	1,700	1,700
Current portion of deferred revenue	14,232	34,705
Current portion of deferred gain on sale leaseback	552	552
Total current liabilities	26,647	48,889
Deferred revenue, net of current portion	25,733	37,097
Deferred gain on sale leaseback, net of current portion	784	1,336
Total liabilities	53,164	87,322
Commitments and contingencies (Note 12)
Stockholders' equity:
Preferred stock, $0.01 par value; 1,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.01 par value; 100,000,000 shares authorized; 62,399,827 and 53,825,567 shares issued and outstanding at December 31, 2012 and 2011, respectively	624	538
Additional paid-in capital	500,655	438,677
Accumulated other comprehensive income (loss)	102	(6)
Accumulated deficit	(420,352)	(409,480)
Total stockholders' equity	81,029	29,729
Total liabilities and stockholders' equity	$ 134,193	$ 117,051