Pension Plan and Postretirement Benefits Other Than Pension (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 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
Employer contributions	$ 3,700
Components of net periodic benefit cost:
Interest cost		$ 439	$ 1,537	$ 3,071	$ 4,610
Expected return on plan assets		(374)	(1,579)	(2,618)	(4,736)
Settlement loss		1,272		1,272
Total		1,337	(42)	$ 1,725	(126)
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	9	$ 12	25
Actuarial gain amortization		(67)	(124)	(201)	(371)
Total		$ (63)	$ (115)	$ (189)	$ (346)