Reclassification out of accumulated other comprehensive loss (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Interest expense	$ (119,273)	$ (93,984)	$ (96,519)
Income taxes	(94,783)	(88,920)	(84,590)
Other income	7,379	26,416	26,711
Net income	367,489	378,131	$ 390,205
Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Net income	(2,346)	(2,450)
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	(590)	(591)
Income taxes	177	145
Net income	(413)	(446)
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	597	615
Other income	(2,416)	(2,485)
Net income	(1,819)	(1,870)
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	31	36
Other income	(145)	(170)
Net income	$ (114)	$ (134)