CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS
Alliance revenue	$ 163	$ 187	$ 418	$ 565
Operating expenses:
Research and development	10,880	17,891	24,436	29,376
General and administrative	5,583	3,888	12,562	7,969
Total operating expenses	16,463	21,779	36,998	37,345
Loss from operations	(16,300)	(21,592)	(36,580)	(36,780)
Other income (expense):
Interest income	271	144	482	297
Interest expense	(4)	(13)	(11)	(29)
Foreign currency exchange gain (loss)	2	(10)	(17)	(16)
Net loss	$ (16,031)	$ (21,471)	$ (36,126)	$ (36,528)
Net loss per share applicable to common stockholders - basic and diluted (Note 11)	$ (0.59)	$ (1.15)	$ (1.39)	$ (1.96)
Weighted-average number of common shares used in computing net loss per share applicable to common stockholders - basic and diluted	27,133	18,676	26,012	18,657
Comprehensive loss:
Net loss	$ (16,031)	$ (21,471)	$ (36,126)	$ (36,528)
Unrealized gain on available-for-sale securities				16
Total other comprehensive income				16
Comprehensive loss	$ (16,031)	$ (21,471)	$ (36,126)	$ (36,512)