Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 456,535	$ 758,505
Marketable securities	665,041	531,604
Tenant improvement receivable	19	3,112
Prepaid expenses	28,267	21,171
Receivables and other current assets	14,246	8,377
Total current assets	1,164,108	1,322,769
Marketable securities	444,782	324,193
Property, plant and equipment, net	204,230	199,606
Intangible assets, net	15,991	16,931
Goodwill	13,128	13,128
Restricted cash and other non-current assets	24,569	23,940
Total assets	1,866,808	1,900,567
Current Liabilities:
Accounts payable	12,028	12,873
Accrued expenses and other current liabilities	61,688	57,065
Deferred revenue, current portion	34,040	25,674
Total current liabilities	107,756	95,612
Deferred revenue, net of current portion	28,806	21,763
Contingent consideration	2,765	2,231
Financing lease obligation, net of current portion	154,545	154,749
Other non-current liabilities	2,735	2,780
Total liabilities	296,607	277,135
Commitments and contingencies (Note 7)
Stockholders’ Equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at March 31, 2018 and December 31, 2017
Common stock, $0.01 par value, 125,000 shares authorized; 50,067 and 49,406 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	501	494
Additional paid-in capital	2,633,057	2,540,951
Accumulated other comprehensive loss	(5,049)	(4,205)
Accumulated deficit	(1,058,308)	(913,808)
Total stockholders’ equity	1,570,201	1,623,432
Total liabilities and stockholders’ equity	$ 1,866,808	$ 1,900,567