Pension Plan and Postretirement Benefits Other Than Pension (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
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	$ 1,537	$ 1,497	$ 4,610	$ 4,490
Expected return on plan assets	(1,579)	(2,065)	(4,736)	(6,196)
Total	(42)	(568)	$ (126)	(1,706)
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	9	14	$ 25	41
Actuarial gain amortization	(124)	(30)	(371)	(90)
Prior service cost amortization		(1)		(2)
Total	$ (115)	$ (17)	$ (346)	$ (51)