Basis of presentation and significant accounting policies - Net effect of transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Purchased oil
Disaggregation of Revenue [Line Items]
Net effect on earnings	$ (837)	$ 364	$ 1,214
Sales of purchased oil inventory
Disaggregation of Revenue [Line Items]
Net effect on earnings	494,860	104,403	327,839
Purchased oil inventory
Disaggregation of Revenue [Line Items]
Net effect on earnings	$ 495,697	$ 104,039	$ 326,625