Pension Plan and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pension Plan
Pension Plan and Other Postretirement Benefits
Employer cash contributions			$ 2,900	$ 12,400
Estimated cash contributions in the current fiscal year	$ 2,900		2,900
Components of the pension plans and other postretirement benefits
Service cost	6,046	$ 9,235	18,137	27,704
Interest cost	8,746	6,329	26,238	18,986
Expected return on plan assets	(13,421)	(11,307)	(40,263)	(33,920)
Amortization of prior service cost	131	242	394	727
Recognized net actuarial (gain) loss	(637)	999	(1,911)	2,997
Net periodic benefit cost (credit)	865	5,498	2,595	16,494
Other Benefits
Pension Plan and Other Postretirement Benefits
Employer cash contributions			200	500
Estimated cash contributions in the current fiscal year	200		200
Components of the pension plans and other postretirement benefits
Service cost	1,126	1,683	3,379	5,048
Interest cost	1,297	1,008	3,892	3,024
Expected return on plan assets	(2,636)	(2,482)	(7,907)	(7,445)
Amortization of prior service cost	39	39	116	117
Recognized net actuarial (gain) loss	(581)	(228)	(1,744)	(685)
Net periodic benefit cost (credit)	$ (755)	$ 20	$ (2,264)	$ 59