Postretirement Benefits - Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair value of plan assets:
Fair value of plan assets, beginning of year	$ 829,866	$ 1,140,243
Actual return on plan assets	105,631	(304,005)
Employer contributions	96,222	25,764
Benefits paid	(34,840)	(32,136)
Fair value of plan assets, end of year	$ 996,879	$ 829,866