CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 69,987	$ 61,349
Marketable securities	304,882	130,180
Accounts receivable	11,060	7,427
Unbilled revenue	1,969	2,909
Prepaid expenses and other current assets	3,329	3,465
Total current assets	391,227	205,330
Property and equipment, net	22,370	25,422
Restricted cash	20,660	20,719
Intangible assets, net	3,793	4,589
Other long-term assets	156	156
Total assets	438,206	256,216
Current liabilities:
Accounts payable	5,719	7,433
Accrued expenses	14,127	10,348
Deferred revenue	9,770	5,490
Other current liabilities	543	518
Total current liabilities	30,159	23,789
Deferred revenue, net of current portion	14,656	25,508
Other long-term liabilities	129	551
Total liabilities	$ 44,944	$ 49,848
Commitments and contingencies (Note 9)
Stockholders' Equity:
Preferred stock, $0.01 par value per share; 5,000 shares authorized at September 30, 2015 and December 31, 2014, 100 shares of Series A Junior Participating Preferred Stock, $0.01 par value per share designated and no shares issued and outstanding
Common stock, $0.0001 par value per share; 100,000 shares authorized at September 30, 2015 and December 31, 2014, 68,995 shares issued and 68,876 shares outstanding at September 30, 2015 and 54,486 shares issued and outstanding at December 31, 2014	$ 6	$ 5
Additional paid-in capital	818,496	575,438
Accumulated other comprehensive income (loss)	16	(16)
Accumulated deficit	(423,208)	(369,059)
Treasury stock, at cost, 119 shares and zero shares at September 30, 2015 and December 31, 2014, respectively	(2,048)
Total stockholders' equity	393,262	206,368
Total liabilities and stockholders' equity	$ 438,206	$ 256,216