Shareholders' Equity - Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands		3 Months Ended						9 Months Ended
	Jan. 26, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance		$ 118,830	$ 107,816	$ 131,971	$ 192,852	$ (53,542)	$ (45,033)	$ 131,971	$ (45,033)
Beneficial conversion feature on Series A preferred shares			0	0		(8,006)	12,006	0	12,006
Accretion of beneficial conversion feature on Series A preferred shares		0		0	0		(4,000)	0	(12,006)
Issuance of common shares as payment for equity investment				0			352	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
Issuance of common shares as payment for license agreement		4,080			0
Exercise of stock options		602	833	1,003	0	0	0
Share-based compensation expense		3,742	5,608	3,088	6,256	2,663	1,886
Net loss		(61,441)	(39,269)	(85,462)	(42,915)	(38,440)	(18,753)	(186,172)	(100,108)
Shareholders' equity, ending balance		$ 65,813	118,830	107,816	$ 156,193	192,852	(53,542)	$ 65,813	$ 156,193
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			$ 43,842	$ 52,013		$ 0	$ 0