CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 316,608	$ 645,361
Marketable debt securities	905,222	1,045,257
Marketable equity securities	15,004
Accounts receivable, net	3,362	34,002
Inventory	11,081
Prepaid expenses and other current assets	90,843	40,120
Total current assets	1,342,120	1,764,740
Marketable debt securities		13,919
Property, plant and equipment, net	272,652	181,900
Restricted investments	44,825	30,000
Other assets	16,057	4,171
Total assets	1,675,654	1,994,730
Current liabilities:
Accounts payable	21,772	28,355
Accrued expenses	93,564	72,203
Deferred rent	2,723	1,988
Deferred revenue	3,444	41,705
Total current liabilities	121,503	144,251
Deferred rent, net of current portion	40,074	6,626
Deferred revenue, net of current portion	1,623	43,075
Long-term debt	30,000	30,000
Other liabilities	4,335	4,347
Total liabilities	197,535	228,299
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.01 par value per share, 5,000,000 shares authorized and no shares issued and outstanding at September 30, 2018 and December 31, 2017
Common stock, $0.01 par value per share, 125,000,000 shares authorized; 100,968,096 shares issued and outstanding at September 30, 2018; 99,666,549 shares issued and outstanding at December 31, 2017	1,009	997
Additional paid-in capital	4,140,033	3,947,552
Accumulated other comprehensive loss	(33,392)	(34,433)
Accumulated deficit	(2,629,531)	(2,147,685)
Total stockholders’ equity	1,478,119	1,766,431
Total liabilities and stockholders’ equity	$ 1,675,654	$ 1,994,730