CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 61,461	$ 61,349
Marketable securities	288,583	130,180
Accounts receivable	19,385	7,427
Unbilled revenue	1,800	2,909
Prepaid expenses and other current assets	3,479	3,465
Total current assets	374,708	205,330
Property and equipment, net	21,896	25,422
Restricted cash	20,660	20,719
Intangible assets, net	3,528	4,589
Other long-term assets	248	156
Total assets	421,040	256,216
Current liabilities:
Accounts payable	4,053	7,433
Accrued expenses	24,499	10,348
Deferred revenue	9,770	5,490
Other current liabilities	460	518
Total current liabilities	38,782	23,789
Deferred revenue, net of current portion	12,213	25,508
Other long-term liabilities	69	551
Total liabilities	$ 51,064	$ 49,848
Commitments and contingencies (Note 14)
Stockholders' Equity:
Preferred stock, $0.01 par value per share; 5,000 shares authorized at December 31, 2015 and 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 December 31, 2015 and 2014, 69,077 and 54,486 shares issued and outstanding at December 31, 2015 and 2014, respectively	$ 7	$ 5
Additional paid-in capital	824,385	575,438
Accumulated other comprehensive income (loss)	4	(16)
Accumulated deficit	(452,372)	(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	369,976	206,368
Total liabilities and stockholders' equity	$ 421,040	$ 256,216