Net income (loss) per common share - Summary (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income (numerator):
Net income (loss)	$ 216,276	$ 136,832	$ (132,661)	$ (75,439)	$ (165,932)	$ (237,432)	$ (545,455)	$ 74,646	$ 145,008	$ (874,173)	$ (342,459)
Weighted-average common shares outstanding (denominator):
Basic (shares)									14,240	11,668	11,565
Diluted (shares)									14,464	11,668	11,565
Net income (loss) per common share:
Basic (USD per share)	$ 13.07	$ 8.68	$ (10.47)	$ (6.33)	$ (14.18)	$ (20.32)	$ (46.75)	$ 6.43	$ 10.18	$ (74.92)	$ (29.61)
Diluted (USD per share)	$ 12.84	$ 8.56	$ (10.47)	$ (6.33)	$ (14.18)	$ (20.32)	$ (46.75)	$ 6.39	$ 10.03	$ (74.92)	$ (29.61)
Non-vested restricted stock awards
Weighted-average common shares outstanding (denominator):
Non-vested and outstanding awards (shares)									181	0	0
Performance share awards
Weighted-average common shares outstanding (denominator):
Non-vested and outstanding awards (shares)									43	0	0