Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Research and Development Expense [Member]
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	$ 138	$ 11	$ 247	$ 21
General and Administrative Expense [Member]
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	338	21	636	28
Research and development	3,090	1,596	5,723	2,785
General and administrative	1,891	912	3,878	1,656
Total operating expenses	4,981	2,508	9,601	4,441
Loss from operations	(4,981)	(2,508)	(9,601)	(4,441)
Investment income	$ 37	3	$ 77	3
Interest expense		(29)		(857)
Other expense	$ (128)	(29)	$ (128)	(99)
Total other expense	(91)	(55)	(51)	(953)
Net loss	(5,072)	(2,563)	(9,652)	(5,394)
Unrealized gain (loss) on available-for-sale investments	3	(23)	9	(23)
Comprehensive loss	(5,069)	(2,586)	(9,643)	(5,417)
Net loss	$ (5,072)	(2,563)	$ (9,652)	(5,394)
Accretion of redeemable convertible preferred stock to redemption value		(1,897)		(3,409)
Net loss attributable to common stockholders	$ (5,072)	$ (4,460)	$ (9,652)	$ (8,803)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.31)	$ (18.55)	$ (0.59)	$ (36.64)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)	16,449,937	240,374	16,449,316	240,254
Allocated share-based compensation	$ 476	$ 32	$ 883	$ 49
Included in other expense, above, are the following amounts from forward foreign currency contracts:
Realized losses from forward foreign currency contracts	(14)		(14)
Unrealized losses from forward foreign currency contracts	(112)		(112)
Total	$ (126)		$ (126)