Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
CURRENT ASSETS:
Cash and cash equivalents (Note 5)	$ 150,180	$ 29,154
Short-term investments (Note 4)		10,010
Prepaid expenses and other current assets (Note 5)	1,673	561
Total current assets	151,853	39,725
Property and equipment, net (Note 5)	566	214
Other assets	349	626
TOTAL ASSETS	152,768	40,565
CURRENT LIABILITIES:
Accrued liabilities (Note 5)	7,016	1,473
Accounts payable	358	622
Other current liabilities	23
Total current liabilities	7,397	2,095
Preferred stock warrant liabilities (Note 10)		1,810
Other liabilities		100
TOTAL LIABILITIES	$ 7,397	$ 4,005
Commitments and Contingencies (Note 7)
Convertible preferred stock value		$ 144,375
STOCKHOLDERS' EQUITY (DEFICIT):
Preferred stock (Note 9), $0.001 par value; 10,000,000 and nil shares authorized as of December 31, 2015 and December 31, 2014; nil shares issued and outstanding as of December 31, 2015 and December 31, 2014
Common stock, $0.001 par value; 500,000,000 and 180,000,000 shares authorized as of December 31, 2015 and 2014; 30,058,105 and 1,588,701 shares issued and outstanding as of December 31, 2015 and 2014	$ 30	$ 2
Additional paid-in capital	679,528
Accumulated other comprehensive loss		(10)
Accumulated deficit	(534,187)	(107,807)
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	145,371	(107,815)
TOTAL LIABILITIES, CONVERTIBLE AND REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT)	$ 152,768	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