Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
CURRENT ASSETS:
Cash and cash equivalents	$ 133,829	$ 100,348
Prepaid expenses and other current assets	2,159	1,377
Total current assets	135,988	101,725
Property and equipment, net	144	154
Other assets	303	319
TOTAL ASSETS	136,435	102,198
CURRENT LIABILITIES:
Accrued liabilities	4,898	6,133
Accounts payable	740	1,339
Total current liabilities	5,638	7,472
TOTAL LIABILITIES	5,638	7,472
Commitments and Contingencies (Note 6)	0
STOCKHOLDERS' EQUITY:
Preferred stock, $0.001 par value; 10,000,000 shares authorized as of March 31, 2018 and December 31, 2017; nil shares issued and outstanding as of March 31, 2018 and December 31, 2017
Common stock, $0.001 par value; 500,000,000 shares authorized as of March 31, 2018 and December 31, 2017; 74,309,681 and 52,395,223 shares issued and outstanding as of March 31, 2018 and December 31, 2017	74	52
Additional paid-in capital	766,325	718,751
Accumulated deficit	(635,602)	(624,077)
TOTAL STOCKHOLDERS' EQUITY	130,797	94,726
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 136,435	$ 102,198