Postretirement Benefit Plans (Assumptions Used) (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Postretirement Health And Life Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate	2.25%	3.00%
Defined benefit plan, assumptions used calculating benefit obligation, Rate of compensation increase	2.00%	2.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost, Discount rate	3.00%	4.00%	3.50%
Defined benefit plan, assumptions used calculating net periodic benefit cost, Rate of compensation increase	2.00%	3.00%	2.50%
Director's Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate	2.25%	3.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost, Discount rate	2.25%	3.00%	4.00%
Defined benefit plan, assumptions used calculating benefit obligation, Change in consumer price index	1.00%	1.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost, Changes in consumer price index	1.00%	1.00%	2.00%
Scottdale Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate	2.50%	3.25%
Defined benefit plan, assumptions used calculating benefit obligation, Rate of compensation increase	2.50%	3.00%
Defined benefit plan, assumptions used calculating benefit obligation, Expected long-term return on plan assets	4.50%	5.00%