Postretirement Benefit Plans (Plan Assets at Fair Value) (Details) - Scottdale Defined Benefit Pension Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 4,939	$ 5,404	$ 4,818
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	3,409	4,701
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	1,530	703
Cash and Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	522	2,797
Mining [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	23	34
Manufacturing [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	807	830
Transportation, Communications, Electric, Gas, and Sanitary Services [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	555	543
Wholesale Trade [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	17
Finance, Insurance, and Real Estate [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	1,348	330
Services [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	137	155
Other [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets		12
Corporate debt securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 1,530	$ 703