Pension and Other Postretirement Benefit Plans (Schedule of Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 668,481	$ 578,347
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	97	101
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	97	101
Cash/Accrued Income | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	97	101
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
Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	668,384	578,246
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