Business segment data - Operating Revenues Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 1,047,545	$ 1,091,126	$ 2,261,370	$ 2,521,224
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,056,960	1,099,140	2,301,252	2,555,606
Corporate, Non-Segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,418	3,151	2,850	4,723
Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ (10,833)	$ (11,165)	$ (42,732)	$ (39,105)