CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 26,514	$ 52,990
Marketable securities	273,646	287,613
Accounts receivable	3,099	10,811
Unbilled revenue	1,468	800
Prepaid expenses and other current assets	4,341	4,953
Total current assets	309,068	357,167
Property and equipment, net	22,383	22,380
Restricted cash	19,971	19,971
Intangible assets, net	6,181	6,711
Other long-term assets	156	400
Total assets	357,759	406,629
Current liabilities:
Accounts payable	2,751	3,580
Accrued expenses	9,554	9,641
Deferred revenue	4,234	4,426
Other current liabilities	290	514
Total current liabilities	16,829	18,161
Deferred revenue, net of current portion	25,412	27,269
Other long-term liabilities	602	712
Total liabilities	42,843	46,142
Commitments and contingencies (Note 8)
Stockholders' Equity:
Common stock, $0.0001 par value per share; 100,000 shares authorized at June 30, 2013 and December 31, 2012, 51,984 and 51,709 shares issued and outstanding at June 30, 2013 and December 31, 2012, respectively	5	5
Additional paid-in capital	529,905	522,422
Accumulated other comprehensive income	22	111
Accumulated deficit	(215,016)	(162,051)
Total stockholders' equity	314,916	360,487
Total liabilities and stockholders' equity	357,759	406,629
Preferred stock
Stockholders' Equity:
Preferred stock
Series A Junior Participating Preferred Stock
Stockholders' Equity:
Preferred stock