Accumulated Other Comprehensive Income (Loss) - Schedule of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	$ 1,467,448	$ 1,463,994	$ 1,479,456	$ 1,365,580
Tax effect	2,002	12,920	5,721	50,058
Ending Balance	1,450,565	1,425,564	1,450,565	1,425,564
Accumulated Other Comprehensive Income (loss)
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	37,200	59,158	38,782	61,429
Unrealized gains			17
Amounts reclassified from accumulated other comprehensive income			(4,020)
Tax effect			852
Ending Balance	35,631	$ 56,880	35,631	$ 56,880
Pension, Postretirement and Other Post-Employment Benefits
Accumulated Other Comprehensive Income (Loss)
Beginning Balance			38,783
Amounts reclassified from accumulated other comprehensive income			(4,012)
Tax effect			854
Ending Balance	35,625		35,625
Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss)
Beginning Balance			(1)
Unrealized gains			17
Amounts reclassified from accumulated other comprehensive income			(8)
Tax effect			(2)
Ending Balance	$ 6		$ 6