Pension and Other Postretirement Benefit Plans (Schedule of Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets) (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 720,098	$ 644,142
Accumulated benefit obligation	719,985	644,069
Fair value of plan assets	$ 668,481	$ 578,347