Condensed Combined and Consolidated Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Expenses:
Research and development	$ 4,241	$ 1,134	$ 9,332	$ 2,057
Research and development costs paid to Amgen		550	1,066	550
General and administrative	1,708	868	7,162	2,591
Total operating expenses	5,949	2,552	17,560	5,198
Loss from operations	(5,949)	(2,552)	(17,560)	(5,198)
Interest income	30	3	59	8
Loss before provision for income taxes	(5,919)	(2,549)	(17,501)	(5,190)
Provision (benefit) for income taxes		(13)	(22)	27
Net loss	(5,919)	(2,536)	(17,479)	(5,217)
Other comprehensive loss, net of tax:
Unrealized losses on investments	(11)		(11)
Other comprehensive loss	(11)		(11)
Comprehensive loss	$ (5,930)	$ (2,536)	$ (17,490)	$ (5,217)
Net loss per common share:
Basic and diluted net loss per common share	$ (4.20)	$ (2.59)	$ (13.07)	$ (5.73)
Weighted-average common shares outstanding - basic and diluted	1,410,507	977,778	1,337,501	910,839