CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets
Cash and cash equivalents	$ 57,899	$ 6,889
Investment securities, available-for-sale	50,068	24,159
Prepaid expenses, receivables and other current assets	581	901
Total current assets	108,548	31,949
Property and equipment, net	42	151
Other assets		14
Total assets	108,590	32,114
Liabilities, redeemable common stock and stockholders' equity
Accounts payable	1,375	1,960
Accrued expenses	4,139	3,504
Current portion of deferred revenue	434	669
Current portion of long-term debt		32
Total current liabilities	5,948	6,165
Long-term portion of deferred revenue		2,587
Total liabilities	5,948	8,752
Commitments and contingencies (Note 10)
Stockholders' equity
Preferred stock, $0.0001 par value; 5,000,000 shares authorized at December 31, 2012 and 2011; no shares issued and outstanding at December 31, 2012 and 2011
Common stock, $0.0001 par value; 150,000,000 shares authorized at December 31, 2012 and 2011; 73,334,216 shares and 52,898,659 shares issued and outstanding at December 31, 2012 and 2011, respectively	7	5
Additional paid-in capital	452,693	370,219
Accumulated deficit	(367,720)	(346,871)
Accumulated other comprehensive income	4	9
Total stockholders' equity	84,984	23,362
Total liabilities, redeemable common stock and stockholders' equity	108,590	32,114
Redeemable Common Stock
Liabilities, redeemable common stock and stockholders' equity
Redeemable common stock, $0.0001 par value; 5,347,137 shares and no shares issued and outstanding at December 31, 2012 and 2011, respectively (Note 7)	$ 17,658