Segment Information (Schedule of Reconciliation of Total Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Property, Plant and Equipment, Net	$ 2,122,297	$ 2,180,270	$ 2,325,181
ASSETS
Segment Assets	2,707,099	2,687,434	$ 2,867,733
Items excluded from segment assets:
Deferred tax assets	277,887	521,199
Operating Segments | Segment assets for total reportable business segments
ASSETS
Segment Assets	1,971,268	1,982,206
Operating Segments | Segment assets for all other business segments
ASSETS
Segment Assets	508,334	520,586
Corporate Reconciling Items And Eliminations
Items excluded from segment assets:
Cash and other investments	152,432	63
Deferred tax assets	$ 75,065	$ 184,579