Shareholders' Equity - Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 26, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance				$ 131,971	$ (45,033)
Beneficial conversion feature on Series A preferred shares				0	12,006
Accretion of beneficial conversion feature on Series A preferred shares		$ 0	$ (8,006)	0	(12,006)
Issuance of common shares as payment for equity investment				0	352
Conversion of convertible preferred shares to common shares				0	81,936
Issuance of common shares in settlement of contingent equity liability				0	32,020
Issuance of common share warrant as consideration for services				0	93
Reclassification of warrant liability to equity	$ 5,203			5,203	0
Exercise of stock options				1,836	0
Share-based compensation expense				8,696	4,549
Net loss		(39,269)	(38,440)	(124,731)	(57,193)
Shareholders' equity, ending balance		$ 118,830	$ 192,852	118,830	192,852
Initial Public Offering
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares, net of offering costs				0	176,128
Private Placement
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares, net of offering costs				$ 95,855	$ 0