Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 46,656	$ 24,840
Marketable securities	114,122	64,714
Accounts receivable	473	1,032
Prepaid expenses	5,334	1,775
Other current assets	1,412	1,010
Total current assets	167,997	93,371
Marketable securities	15,616	69,412
Property and equipment, net	13,977	9,324
Restricted cash	225	225
Other assets	862	400
Total assets	198,677	172,732
Current liabilities
Accounts payable	4,832	1,543
Accrued expenses and other current liabilities	9,605	8,126
Total current liabilities	14,437	9,669
Deferred rent, net of current portion	1,211	1,326
Total liabilities	15,648	10,995
Commitments and contingencies (Note 6)
Stockholders’ equity
Preferred stock; $0.0001 par value; 10,000 shares authorized, and no shares issued and outstanding at December 31, 2017 and December 31, 2016
Common stock; $0.0001 par value; 100,000 shares authorized at December 31, 2017 and December 31, 2016; 31,295 and 26,477 shares issued and outstanding at December 31, 2017 and December 31, 2016, respectively	3	3
Additional paid-in capital	371,497	276,354
Accumulated other comprehensive loss	(715)	(33)
Accumulated deficit	(187,756)	(114,587)
Total stockholders’ equity	183,029	161,737
Total liabilities and stockholders’ equity	$ 198,677	$ 172,732