Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
CURRENT ASSETS:
Cash and cash equivalents (Note 5)	$ 140,871	$ 150,180
Prepaid expenses and other current assets (Note 5)	1,746	1,673
Total current assets	142,617	151,853
Property and equipment, net (Note 5)	623	566
Other assets	196	349
TOTAL ASSETS	143,436	152,768
CURRENT LIABILITIES:
Accrued liabilities (Note 5)	5,342	7,016
Accounts payable	1,779	358
Other current liabilities	7	23
Total current liabilities	7,128	7,397
TOTAL LIABILITIES	$ 7,128	$ 7,397
Commitments and Contingencies (Note 6)
STOCKHOLDERS' EQUITY (DEFICIT):
Preferred stock, $0.001 par value; 10,000,000 shares authorized as of March 31, 2016 and December 31, 2015; nil shares issued and outstanding as of March 31, 2016 and December 31, 2015
Common stock, $0.001 par value; 500,000,000 shares authorized as of March 31, 2016 and December 31, 2015; 30,174,778 and 30,058,105 shares issued and outstanding as of March 31, 2016 and December 31, 2015	$ 30	$ 30
Additional paid-in capital	681,003	679,528
Accumulated deficit	(544,725)	(534,187)
TOTAL STOCKHOLDERS' EQUITY	136,308	145,371
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 143,436	$ 152,768