Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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	$ 650	$ 114	$ 106
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	$ 1,514	345	$ 49
Revenue		2,948
Research and development	$ 12,381	6,432	$ 3,994
General and administrative	8,489	4,096	3,128
Total operating expenses	20,870	10,528	7,122
Loss from operations	(20,870)	(7,580)	(7,122)
Investment income	$ 144	24	4
Interest expense		(857)	(861)
Other (expense) income, net	$ (651)	5,071	67
Total other (expense) income	(507)	4,238	(790)
Net loss	(21,377)	(3,342)	(7,912)
Unrealized loss on available-for-sale investments	(5)	(6)	(1)
Comprehensive loss	(21,382)	(3,348)	(7,913)
Net loss	$ (21,377)	(3,342)	(7,912)
Accretion of redeemable convertible preferred stock to redemption value		(6,353)	(6,119)
Net loss attributable to common stockholders	$ (21,377)	$ (9,695)	$ (14,031)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (1.30)	$ (3.16)	$ (59.66)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)	16,464,123	3,064,507	235,184
Allocated share-based compensation	$ 2,164	$ 459	$ 155
Included in other expense, above, are the following amounts from forward foreign currency contracts:
Realized losses from forward foreign currency contracts	(52)
Unrealized losses from forward foreign currency contracts	(537)
Total	$ (589)