Employee benefit plans - Schedule of Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Pension benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Interest cost	$ 3,303	$ 3,200	$ 6,606	$ 6,400
Expected return on assets	(3,645)	(4,028)	(7,290)	(8,056)
Amortization of net actuarial gain (loss)	1,194	1,037	2,387	2,074
Net periodic benefit cost (credit)	852	209	1,703	418
Other postretirement benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	99	126	198	252
Interest cost	462	459	924	918
Expected return on assets	(1,292)	(1,329)	(2,584)	(2,658)
Amortization of prior service credit	(289)	(330)	(579)	(660)
Amortization of net actuarial gain (loss)	(80)	(72)	(160)	(144)
Net periodic benefit credit, including amount capitalized	(1,100)	(1,146)	(2,201)	(2,292)
Less amount capitalized	18	47	36	69
Net periodic benefit cost (credit)	$ (1,118)	$ (1,193)	$ (2,237)	$ (2,361)