New Accounting Principles and Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2018	Jun. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of certain tax effects from accumulated other comprehensive loss to retained earnings		$ (30,237)
Accounting Standards Update 2018-02 [Member] | Retirement and Postretirement Benefit Plan Adjustments [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of certain tax effects from accumulated other comprehensive loss to retained earnings	$ 28,400
Accounting Standards Update 2018-02 [Member] | Deferred Loss On Interest Rate Derivative Hedges [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of certain tax effects from accumulated other comprehensive loss to retained earnings		$ 1,800