Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue			$ 2,948
Operating expenses:
Research and development	18,869	12,381	6,432
General and administrative	9,836	8,489	4,096
Total operating expenses	28,705	20,870	10,528
Loss from operations	(28,705)	(20,870)	(7,580)
Other income (expense):
Investment income	193	144	24
Interest expense			(857)
Other (expense) income, net	(14)	(651)	5,071
Total other income (expense)	179	(507)	4,238
Net loss	(28,526)	(21,377)	(3,342)
Unrealized gain (loss) on short term investments	11	(5)	(6)
Comprehensive loss	(28,515)	(21,382)	(3,348)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(28,526)	(21,377)	(3,342)
Accretion of redeemable convertible preferred stock to redemption value			(6,353)
Net loss attributable to common stockholders	$ (28,526)	$ (21,377)	$ (9,695)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (1.72)	$ (1.30)	$ (3.16)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)	16,561,799	16,464,123	3,064,507
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	$ 3,343	$ 2,164	$ 459
Included in other expense, above, are the following amounts from forward foreign currency contracts:
Realized losses from forward foreign currency contracts	(61)	(52)
Unrealized gains (losses) from forward foreign currency contracts	127	(537)
Total	66	(589)
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	1,114	650	114
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	$ 2,229	$ 1,514	$ 345