Employee benefit plans - Schedule of Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Pension benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Interest cost	$ 3,303	$ 3,200	$ 9,909	$ 9,600
Expected return on assets	(3,645)	(4,028)	(10,935)	(12,084)
Amortization of net actuarial gain (loss)	1,193	1,037	3,580	3,111
Net periodic benefit cost (credit)	851	209	2,554	627
Other postretirement benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	99	126	297	378
Interest cost	462	459	1,386	1,377
Expected return on assets	(1,292)	(1,329)	(3,876)	(3,987)
Amortization of prior service credit	(290)	(330)	(869)	(990)
Amortization of net actuarial gain (loss)	(80)	(72)	(240)	(216)
Net periodic benefit credit, including amount capitalized	(1,101)	(1,146)	(3,302)	(3,438)
Less amount capitalized	18	25	54	72
Net periodic benefit cost (credit)	$ (1,119)	$ (1,171)	$ (3,356)	$ (3,510)