Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Collaboration revenue	[1]	$ 5,164	$ 247
Operating expenses:
Research and development	[2]	42,238	12,573	$ 1,513
General and administrative		31,056	13,403	5,114
Total operating expenses		73,294	25,976	6,627
Loss from operations		(68,130)	(25,729)	(6,627)
Other income (expense):
Interest expense		(8,050)	(108)
Loss from equity method investment		(36,532)
Gain on extinguishment of convertible loan		11,482
Other income (expense), net		78,512	16	(236)
Total other income (expense), net		45,412	(92)	(236)
Net loss before (provision for) benefit from income taxes		(22,718)	(25,821)	(6,863)
(Provision for) benefit from income taxes		(484)	(7)	63
Net loss		(23,202)	(25,828)	(6,800)
Foreign currency translation adjustment		(18)	(6)	(2)
Comprehensive loss		(23,220)	(25,834)	(6,802)
Reconciliation of net loss to net loss attributable to common shareholders:
Net loss		(23,202)	(25,828)	(6,800)
Loss attributable to noncontrolling interest		25	325	536
Loss on extinguishment of redeemable convertible preferred shares				(745)
Net loss attributable to common shareholders		$ (23,177)	$ (25,503)	$ (7,009)
Net loss per share attributable to common shareholders—basic and diluted		$ (1.89)	$ (5.06)	$ 1.97
Weighted-average common shares outstanding used in net loss per share attributable to common shareholders—basic and diluted		12,257,483	5,037,404	3,559,985

[1] Including the following amounts of revenue from a related party, see Note 16:

[2] Including the following amounts of research and development from a related party, see Note 16: