Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 43,224	$ 6,414
Short-term investments	83,438	53,817
Prepaid expenses and other current assets	3,002	1,647
Restricted cash	197	0
Total current assets	129,861	61,878
Property and equipment, net	8,313	3,367
Restricted cash	439	197
Other long-term assets	0	130
Total assets	138,613	65,572
Current liabilities:
Accounts payable	3,352	2,520
Accrued expenses and other current liabilities	7,891	7,654
Total current liabilities	11,243	10,174
Other non-current liabilities	520	73
Total liabilities	$ 11,763	$ 10,247
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized, no shares issued and outstanding	$ 0	$ 0
Common stock, $0.001 par value; 100,000,000 shares authorized; 27,296,747 and 24,413,666, shares issued at December 31, 2015 and 2014, respectively; 27,296,747 and 24,084,637 shares outstanding at December 31, 2015 and 2014, respectively	27	24
Additional paid-in capital	294,910	150,025
Accumulated other comprehensive loss	(170)	(26)
Accumulated deficit	(167,917)	(94,698)
Total stockholders' equity	126,850	55,325
Total liabilities and stockholders' equity	$ 138,613	$ 65,572