Pension Plan and Postretirement Benefits Other Than Pension (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits
Pension Plan and Postretirement Benefits Other than Pension
Final number of years of employee's compensation to determine the benefits payable			10 years
Components of net periodic benefit cost:
Interest cost	$ 1,316	$ 1,545	$ 2,632	$ 3,073
Expected return on plan assets	(1,122)	(1,567)	(2,244)	(3,157)
Total	194	(22)	$ 388	(84)
Other Postretirement Benefits
Pension Plan and Postretirement Benefits Other than Pension
Age of employees after which the plan does not provide benefits			65 years
Components of net periodic benefit cost:
Interest cost	4	8	$ 8	16
Actuarial gain amortization	(67)	(123)	(134)	(247)
Total	$ (63)	$ (115)	$ (126)	$ (231)