Convertible Preferred Shares (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended				9 Months Ended
	May 31, 2017	Feb. 28, 2017	Oct. 31, 2016	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Preferred Shares
Accretion of beneficial conversion feature on Series A preferred shares				$ 0	$ 0	$ 0	$ 4,000	$ 0	$ 12,006
Shares issued on conversion of preferred stock (shares)	9,358,560
AstraZeneca
Preferred Shares
Shares issued on conversion of preferred stock (shares)	538,149
Series A Convertible Preferred Shares
Preferred Shares
Preferred stock issued and sold (shares)		4,305,182	4,305,209
Accretion of beneficial conversion feature on Series A preferred shares		$ 2,406
Shares issued on conversion of preferred stock (shares)	9,358,560
Series A Convertible Preferred Shares | AstraZeneca
Preferred Shares
Preferred stock issued and sold (shares)			538,150