Pensions and Other Postretirement Benefit Plans (Schedule of Pension Plans with Projected Benefit Obligation and Accumulated Benefit Obligation in Excess of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Plans with projected benefit obligation in excess of plan assets:
Projected benefit obligation	$ 131,717	$ 121,600
Fair value of plan assets	90,149	83,622
Plans with accumulated benefit obligation in excess of plan assets:
Accumulated benefit obligation	129,698	119,728
Fair value of plan assets	$ 90,149	$ 83,558