Loss per common share - Summary of computation of basic and diluted loss per common share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net loss	$ (39,383)	$ (56,849)
Denominator:
Weighted average common shares for basic loss per common share	347,219	271,460
Effect of dilutive securities	0	0
Weighted average common shares for diluted loss per common share	347,219	271,460
Loss per common share, basic and diluted	$ (0.11)	$ (0.21)