Postretirement Benefit Plans (Plan Assets at Fair Value) (Details) - Defined Benefit Pension Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 4,818	$ 8,121
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	4,268
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	550
Cash and Cash Equivalents [Member] \| Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	2,430
Mining [Member] \| Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	36
Manufacturing [Member] \| Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	888
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	468
Finance, Insurance, and Real Estate [Member] \| Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	248
Services [Member] \| Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	189
Other [Member] \| Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	9
Corporate debt securities [Member] \| Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 550