Earnings (Loss) per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic and diluted loss per share
Net loss for the period	$ (23,045)	$ (17,795)	$ (21,707)	$ (20,217)	$ (30,824)	$ (52,825)	$ (17,788)	$ (13,342)	$ (82,764)	$ (114,780)	$ (74,356)
Weighted average number of shares outstanding									74,199,482	50,795,768	29,830,669
Basic and diluted loss per share	$ (0.29)	$ (0.24)	$ (0.30)	$ (0.29)	$ (0.46)	$ (0.90)	$ (0.44)	$ (0.36)	$ (1.12)	$ (2.26)	$ (2.49)