CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 724,959	$ 420,146
Marketable debt securities	519,578	662,803
Marketable equity securities		1,206
Accounts receivable, net	33,801	18,760
Inventory	32,001	24,068
Prepaid expenses and other current assets	81,674	73,713
Total current assets	1,392,013	1,200,696
Property, plant and equipment, net	341,712	320,658
Operating lease right-of-use assets	226,412
Restricted investments	44,825	44,825
Other assets	9,037	8,623
Total assets	2,013,999	1,574,802
Current liabilities:
Accounts payable	22,671	59,708
Accrued expenses	106,873	112,719
Operating lease liability	16,977
Deferred rent		3,571
Deferred revenue	2,642	3,496
Total current liabilities	149,163	179,494
Operating lease liability, net of current portion	282,300
Deferred rent, net of current portion		57,920
Deferred revenue, net of current portion	478	458
Long-term debt	30,000	30,000
Other liabilities	5,072	4,965
Total liabilities	467,013	272,837
Commitments and contingencies (Note 14)
Stockholders’ equity:
Preferred stock, $0.01 par value per share, 5,000 shares authorized and no shares issued and outstanding at March 31, 2019 and December 31, 2018
Common stock, $0.01 par value per share, 125,000 shares authorized; 106,400 shares issued and outstanding at March 31, 2019; 101,177 shares issued and outstanding at December 31, 2018	1,064	1,011
Additional paid-in capital	4,601,662	4,175,139
Accumulated other comprehensive loss	(32,853)	(33,213)
Accumulated deficit	(3,022,887)	(2,840,972)
Total stockholders’ equity	1,546,986	1,301,965
Total liabilities and stockholders’ equity	$ 2,013,999	$ 1,574,802