Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pensions
Pension and other postretirement benefits expenses
Service cost	$ 1,741	$ 1,649
Interest cost	3,172	3,817
Expected return on plan assets	(6,972)	(7,393)
Amortization of prior service cost	85	80
Amortization of actuarial losses	3,926	3,339
Net periodic benefit cost	1,952	1,492
Other Postretirement Benefits
Pension and other postretirement benefits expenses
Service cost	25	22
Interest cost	206	264
Amortization of prior service cost	7	7
Amortization of actuarial losses	70	23
Net periodic benefit cost	$ 308	$ 316