Reclassification out of accumulated other comprehensive loss (Details 2) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Interest expense	$ (32,129)			$ (20,196)			$ (82,541)	$ (58,275)
Other income	8,918			5,774			29,251	2,521
Income taxes	(13,325)			(4,211)			(92,311)	(28,352)
Net income	74,929	$ 130,692	$ 38,353	147,971	$ 70,667	$ 31,763	243,974	250,401
Reclassification out of accumulated other comprehensive loss
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Net income	(4)			(614)			(598)	(1,800)
Reclassification adjustment for loss on derivative instruments included in net income | Reclassification out of accumulated other comprehensive loss | Interest rate contract
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Interest expense	0			(148)			(98)	(443)
Income taxes	0			37			17	109
Net income	0			(111)			(81)	(334)
Amortization of postretirement liability losses included in net periodic benefit credit | Reclassification out of accumulated other comprehensive loss
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Other income	(92)			(609)			(744)	(1,827)
Income taxes	98			148			263	460
Net income	6			(461)			(481)	(1,367)
Reclassification adjustment on available-for-sale investments included in net income | Reclassification out of accumulated other comprehensive loss
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Other income	(13)			(54)			(45)	(126)
Income taxes	3			12			9	27
Net income	$ (10)			$ (42)			$ (36)	$ (99)