Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
CURRENT ASSETS
Cash and cash equivalents	$ 25,430	$ 22,461
Marketable securities	80,111	52,052
Prepaid expenses and other current assets	4,394	2,158
Total current assets	109,935	76,671
Restricted cash	1,500
Property and equipment, net	921	1,018
Operating lease right-of-use assets	5,018
Other non-current assets	120	50
TOTAL ASSETS	117,494	77,739
CURRENT LIABILITIES
Accounts payable	2,724	663
Operating lease liabilities	328
Accrued and other current liabilities	9,967	9,576
Total current liabilities	13,019	10,239
Non-current operating lease liabilities	4,815
Other non-current liabilities	45	72
TOTAL LIABILITIES	17,879	10,311
Commitments and Contingencies (Note 6 and 10)
STOCKHOLDERS’ EQUITY
Preferred stock, $0.0001 par value; 10,000,000 shares authorized as of June 30, 2019 and December 31, 2018; no shares issued and outstanding as of June 30, 2019 and December 31, 2018
Common stock, $0.0001 par value; 500,000,000 shares authorized as of June 30, 2019 and December 31, 2018; 28,848,303 shares and 24,140,097 shares issued and outstanding as of June 30, 2019 and December 31, 2018, respectively	3	2
Additional paid-in capital	251,592	184,314
Accumulated other comprehensive income (loss)	67	(27)
Accumulated deficit	(152,047)	(116,861)
TOTAL STOCKHOLDERS’ EQUITY	99,615	67,428
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 117,494	$ 77,739