Business segment data - Schedule of Operating Revenues Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Segment Reporting [Line Items]
External operating revenues	$ 375,303	$ 351,186	$ 981,280	$ 1,026,019
Total reportable segment operating revenues
Segment Reporting [Line Items]
External operating revenues	385,565	361,215	1,026,258	1,069,656
Other revenue
Segment Reporting [Line Items]
External operating revenues	201	179	400	358
Elimination of intersegment operating revenues
Segment Reporting [Line Items]
External operating revenues	$ (10,463)	$ (10,208)	$ (45,378)	$ (43,995)

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details