Earnings (Loss) per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic and diluted loss per share
Net loss for the period	$ (21,707)	$ (20,217)	$ (17,788)	$ (13,342)	$ (41,924)	$ (31,130)
Weighted average number of shares outstanding	72,526,441		40,515,920		70,624,583	38,723,718
Basic and diluted loss per share	$ (0.30)		$ (0.44)		$ (0.59)	$ (0.80)