Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 142,423	$ 46,656
Marketable securities	230,166	114,122
Accounts receivable	2,626	473
Prepaid expenses	6,308	5,334
Other current assets	4,834	1,412
Total current assets	386,357	167,997
Marketable securities	102,296	15,616
Accounts receivable	4,600
Property and equipment, net	19,856	13,977
Restricted cash	225	225
Other assets	1,650	862
Total assets	514,984	198,677
Current liabilities
Accounts payable	5,214	4,832
Accrued expenses and other current liabilities	13,306	9,605
Deferred revenue	600
Total current liabilities	19,120	14,437
Deferred rent, net of current portion	1,116	1,211
Other liabilities	691
Total liabilities	20,927	15,648
Commitments and contingencies (Note 6)
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, and no shares issued and outstanding at September 30, 2018 and December 31, 2017
Common stock; $0.0001 par value; 100,000 shares authorized at September 30, 2018 and December 31, 2017; 35,704 and 31,295 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	4	3
Additional paid-in capital	582,249	371,497
Accumulated other comprehensive loss	(874)	(715)
Accumulated deficit	(87,322)	(187,756)
Total stockholders’ equity	494,057	183,029
Total liabilities and stockholders’ equity	$ 514,984	$ 198,677