CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 420,146	$ 645,361
Marketable debt securities	662,803	1,045,257
Marketable equity securities	1,206
Accounts receivable, net	18,760	34,002
Inventory	24,068
Prepaid expenses and other current assets	73,713	40,120
Total current assets	1,200,696	1,764,740
Marketable debt securities		13,919
Property, plant and equipment, net	320,658	181,900
Restricted investments	44,825	30,000
Other assets	8,623	4,171
Total assets	1,574,802	1,994,730
Current liabilities:
Accounts payable	59,708	28,355
Accrued expenses	112,719	72,203
Deferred rent	3,571	1,988
Deferred revenue	3,496	41,705
Total current liabilities	179,494	144,251
Deferred rent, net of current portion	57,920	6,626
Deferred revenue, net of current portion	458	43,075
Long-term debt	30,000	30,000
Other liabilities	4,965	4,347
Total liabilities	272,837	228,299
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.01 par value per share, 5,000,000 shares authorized and no shares issued and outstanding at December 31, 2018 and 2017
Common stock, $0.01 par value per share, 125,000,000 shares authorized; 101,177,007 shares issued and outstanding at December 31, 2018; 99,666,549 shares issued and outstanding at December 31, 2017	1,011	997
Additional paid-in capital	4,175,139	3,947,552
Accumulated other comprehensive loss	(33,213)	(34,433)
Accumulated deficit	(2,840,972)	(2,147,685)
Total stockholders’ equity	1,301,965	1,766,431
Total liabilities and stockholders’ equity	$ 1,574,802	$ 1,994,730