Pension and Other Postretirement Benefit Plans (Schedule of Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 578,347	$ 679,245
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	101	5,214
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash/Accrued Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	101	5,202
Cash/Accrued Income | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	101	5,202
Cash/Accrued Income | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash/Accrued Income | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
US Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	12
US Equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	12
US Equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
US Equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	578,246	674,031
Private Equity Funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private Equity Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private Equity Funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0