Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 57,649	$ 24,840
Marketable securities	104,434	64,714
Accounts receivable	50	1,032
Prepaid expenses	2,432	1,775
Other current assets	1,252	1,010
Total current assets	165,817	93,371
Marketable securities	46,417	69,412
Property and equipment, net	11,524	9,324
Restricted cash	225	225
Other assets	393	400
Total assets	224,376	172,732
Current liabilities
Accounts payable	3,948	1,543
Accrued expenses and other current liabilities	7,514	8,126
Total current liabilities	11,462	9,669
Deferred rent, net of current portion	1,217	1,326
Total liabilities	12,679	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 June 30, 2017 and December 31, 2016
Common stock; $0.0001 par value; 100,000 shares authorized at June 30, 2017 and December 31, 2016; 30,853 and 26,477 shares issued and outstanding at June 30, 2017 and December 31, 2016, respectively	3	3
Additional paid-in capital	363,393	276,354
Accumulated other comprehensive loss	(646)	(33)
Accumulated deficit	(151,053)	(114,587)
Total stockholders’ equity	211,697	161,737
Total liabilities and stockholders’ equity	$ 224,376	$ 172,732