Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
CURRENT ASSETS:
Cash and cash equivalents (Note 5)	$ 157,308	$ 29,154
Short-term investments (Note 4)		10,010
Prepaid expenses and other current assets (Note 5)	1,280	561
Total current assets	158,588	39,725
Property and equipment, net (Note 5)	565	214
Other assets (Note 5)	203	626
TOTAL ASSETS	159,356	40,565
CURRENT LIABILITIES:
Accrued liabilities (Note 5)	2,913	1,473
Accounts payable	849	622
Other current liabilities	38
Total current liabilities	3,800	2,095
Preferred stock warrant liabilities (Note 9)		1,810
Other liabilities		100
TOTAL LIABILITIES	$ 3,800	$ 4,005
Commitments and Contingencies (Note 6)
Convertible preferred stock value		$ 144,375
STOCKHOLDERS' EQUITY (DEFICIT):
Preferred stock, $0.001 par value; 10,000,000 and nil shares authorized as of September 30, 2015 and December 31, 2014 and nil shares issued and outstanding as of September 30, 2015 and December 31, 2014
Common stock, $0.001 par value; 500,000,000 and 180,000,000 shares authorized as of September 30, 2015 and December 31, 2014 and 30,058,105 and 1,588,701 shares issued and outstanding as of September 30, 2015 and December 31, 2014	$ 30	$ 2
Additional paid-in capital	678,255
Accumulated other comprehensive loss		(10)
Accumulated deficit	(522,729)	(107,807)
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	155,556	(107,815)
TOTAL LIABILITIES, CONVERTIBLE AND REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT)	$ 159,356	40,565
Convertible Preferred Stock [Member]
CURRENT LIABILITIES:
Convertible preferred stock value		2,543
Redeemable Convertible Preferred Stock [Member]
CURRENT LIABILITIES:
Convertible preferred stock value		$ 141,832