Earnings (Loss) per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic and diluted loss per share
Net loss for the period	$ (17,795)	$ (21,707)	$ (20,217)	$ (52,825)	$ (17,788)	$ (13,342)	$ (59,719)	$ (83,955)
Weighted average number of shares outstanding	75,161,192			58,442,987			72,153,405	45,369,040
Basic and diluted loss per share	$ (0.24)			$ (0.90)			$ (0.83)	$ (1.85)