Pension Plan and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension Plan
Pension Plan and Other Postretirement Benefits
Employer cash contributions	$ 0	$ 2,900
Estimated cash contributions in the current fiscal year	700
Components of the pension plans and other postretirement benefits
Service cost	5,648	6,046
Interest cost	8,881	8,746
Expected return on plan assets	(13,236)	(13,421)
Amortization of prior service cost	131	131
Recognized net actuarial (gain) loss	189	(637)
Net periodic benefit cost (credit)	1,613	865
Other Benefits
Pension Plan and Other Postretirement Benefits
Employer cash contributions	0	200
Estimated cash contributions in the current fiscal year	200
Components of the pension plans and other postretirement benefits
Service cost	1,520	1,126
Interest cost	1,684	1,297
Expected return on plan assets	(2,987)	(2,636)
Amortization of prior service cost	39	39
Recognized net actuarial (gain) loss	(198)	(581)
Net periodic benefit cost (credit)	$ 58	$ (755)