Retirement Plans, Components of Net Periodic Benefit Cost for the Pension and Postretirement Tables (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
RAP
Net period benefit cost for the pension and postretirement plans
Service cost	$ 1,684	$ 1,853	$ 5,835	$ 6,183
Interest cost	1,682	2,124	4,927	6,139
Expected return on plan assets	(6,395)	(6,386)	(19,256)	(19,196)
Amortization of prior service cost	(19)	(18)	(55)	(55)
Amortization of actuarial loss (gain)	1,346	1,313	3,446	2,923
Total net periodic pension cost	(1,701)	(1,114)	(5,103)	(4,006)
Postretirement Plan
Net period benefit cost for the pension and postretirement plans
Interest cost	13	20	39	59
Amortization of prior service cost	(19)	(19)	(56)	(56)
Total net periodic pension cost	$ (6)	$ 1	$ (17)	$ 2