Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 82,045	$ 24,840
Marketable securities	63,764	64,714
Accounts receivable	228	1,032
Prepaid expenses	1,843	1,775
Other current assets	922	1,010
Total current assets	148,802	93,371
Marketable securities	63,742	69,412
Property and equipment, net	11,061	9,324
Restricted cash	225	225
Other assets	297	400
Total assets	224,127	172,732
Current liabilities
Accounts payable	4,129	1,543
Accrued expenses and other current liabilities	5,829	8,126
Total current liabilities	9,958	9,669
Deferred rent, net of current portion	1,271	1,326
Total liabilities	11,229	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 March 31, 2017 and December 31, 2016
Common stock; $0.0001 par value; 100,000 shares authorized at March 31, 2017 and December 31, 2016; 30,244 and 26,477 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	3	3
Additional paid-in capital	350,047	276,354
Accumulated other comprehensive loss	(572)	(33)
Accumulated deficit	(136,580)	(114,587)
Total stockholders’ equity	212,898	161,737
Total liabilities and stockholders’ equity	$ 224,127	$ 172,732