(Loss) earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
(Loss) earnings per share - basic:
Net (loss) income	$ (60,131)	$ 41,190
Income allocated to participating securities	(21)	(110)
(Loss) income available to common shareholders	$ (60,152)	$ 41,080
Weighted-average shares outstanding	42,028	43,965
(Loss) earnings per share - basic	$ (1.43)	$ 0.93
(Loss) earnings per share - diluted:
Net (loss) income	$ (60,131)	$ 41,190
Income allocated to participating securities	(21)	(65)
Re-measurement of share-based awards classified as liabilities	(775)	0
(Loss) income available to common shareholders	$ (60,927)	$ 41,125
Weighted-average shares outstanding	42,028	43,965
Dilutive impact of potential common shares	37	100
Weighted-average shares and potential common shares outstanding	42,065	44,065
(Loss) earnings per share - diluted	$ (1.45)	$ 0.93
Antidilutive options excluded from calculation	2,214	1,097