Leases (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of Use Asset - Operating Leases (Note 13)	$ 72,632
Operating lease liability	74,892
Gross property, plant and equipment	5,008,180		$ 4,838,171
Accumulated depreciation	2,916,015		$ 2,731,643
Operating lease
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross property, plant and equipment	6,966
Accumulated depreciation	$ 6,966
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of Use Asset - Operating Leases (Note 13)		$ 92,000
Operating lease liability		$ 92,000