Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 146,630	$ 185,323
Marketable securities	182,509
Accounts receivable	679	88
Prepaid expenses and other current assets	2,381	1,772
Total current assets	332,199	187,183
Property and equipment, net	39,442	40,378
Restricted cash and other non-current assets	1,619	1,621
Total assets	373,260	229,182
Current liabilities:
Accounts payable	4,020	4,640
Accrued expenses	11,049	17,439
Notes payable	7,500	10,000
Deferred revenue, current	13,238	256
Other current liabilities	900	748
Total current liabilities	36,707	33,083
Deferred revenue, net of current portion	94,725	26,000
Construction financing lease obligation, net of current portion	33,431	35,096
Other non-current liabilities	317	396
Total liabilities	165,180	94,575
Commitments and contingencies (see note 8)
Stockholders’ equity
Preferred stock, $0.0001 par value per share: 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.0001 par value per share: 195,000,000 shares authorized; 45,025,448 and 36,662,724 shares issued, and 44,507,960 and 35,818,131 shares outstanding at December 31, 2017 and December 31, 2016, respectively	4	4
Additional paid-in capital	514,002	320,129
Accumulated other comprehensive loss	(76)
Accumulated deficit	(305,850)	(185,526)
Total stockholders’ equity	208,080	134,607
Total liabilities and stockholders’ equity	$ 373,260	$ 229,182