Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
CURRENT ASSETS:
Cash and cash equivalents	$ 90,908	$ 106,046
Prepaid expenses and other current assets	3,699	2,706
Total current assets	94,607	108,752
Property and equipment, net	150	168
Operating lease right-of-use asset	716
Other assets	622	549
TOTAL ASSETS	96,095	109,469
CURRENT LIABILITIES:
Accrued and other liabilities	6,619	8,812
Accounts payable	619	1,287
Total current liabilities	7,238	10,099
Term loan	4,763	4,891
Operating lease liabilities	503
TOTAL LIABILITIES	12,504	14,990
Commitments and Contingencies (Note 8)
STOCKHOLDERS' EQUITY:
Preferred stock, $0.001 par value; 10,000,000 shares authorized as of March 31, 2019 and December 31, 2018; nil shares issued and outstanding as of March 31, 2019 and December 31, 2018
Common stock, $0.001 par value; 500,000,000 shares authorized as of March 31, 2019 and December 31, 2018; 74,688,283 and 74,365,965 shares issued and outstanding as of March 31, 2019 and December 31, 2018	74	74
Additional paid-in capital	773,961	771,817
Accumulated deficit	(690,444)	(677,412)
TOTAL STOCKHOLDERS' EQUITY	83,591	94,479
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 96,095	$ 109,469