Reclassification out of accumulated other comprehensive loss (Details 2) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Interest expense	$ (31,369)			$ (23,389)			$ (84,741)	$ (70,224)
Income taxes	(35,318)			(32,748)			(60,847)	(68,860)
Other income	4,769			5,930			(1,877)	18,310
Net income	147,971	$ 70,667	$ 31,763	139,276	$ 100,190	$ 52,131	250,401	291,597
Reclassification out of accumulated other comprehensive loss
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Net income	(614)			(597)			(1,800)	(1,803)
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	(148)			(147)			(443)	(443)
Income taxes	37			36			109	109
Net income	(111)			(111)			(334)	(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]
Income taxes	148			151			460	462
Other income	(609)			(617)			(1,827)	(1,851)
Net income	(461)			(466)			(1,367)	(1,389)
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]
Income taxes	12			6			27	21
Other income	(54)			(26)			(126)	(101)
Net income	$ (42)			$ (20)			$ (99)	$ (80)