Pension Plan and Postretirement Benefits Other Than Pension - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plan and Postretirement Benefits Other than Pension
Defined benefit plan liabilities	$ 446	$ 3,145
Pension Benefits
Pension Plan and Postretirement Benefits Other than Pension
Defined benefit plan assets			$ 8,471
Defined benefit plan liabilities		$ 2,577
Other Postretirement Benefits
Pension Plan and Postretirement Benefits Other than Pension
Initial health care cost trend rate prior to age 65 (as a percent)	6.44%	7.60%	8.05%
Initial health care cost trend rate subsequent to age 65 (as a percent)	7.42%	8.70%	9.30%
Rate to which the cost trend rate is assumed to decline (as a percent)	4.50%
Defined benefit plan liabilities	$ 446	$ 568	$ 798
Current portion of postretirement liability	97	158	$ 250
Other Postretirement Benefits | Other current liabilities
Pension Plan and Postretirement Benefits Other than Pension
Current portion of postretirement liability	$ 100	$ 100