Summary Of Significant Accounting Policies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015
Summary of Significant Accounting Policies [Line Items]
Equity investments, unamortized excess net investment	$ 59,700	$ 61,300
Intangible asset estimated useful life	21 years
Property, Plant and Equipment, Gross	$ 7,235,468	$ 6,783,737
Interest capitalization threshold for construction in process	$ 500
Long-term Debt, Weighted Average Interest Rate, over Time	4.80%	4.90%	4.70%
Deferred Cost Multiplier	0.5
Board of Director Deferred Award Days to Payment	60 days
Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Intangible asset estimated useful life	6 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Intangible asset estimated useful life	30 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Performance Shares [Member]
Summary of Significant Accounting Policies [Line Items]
Equity-based compensation, award payout percentage, minimum	0.00%
Equity-based compensation, award payout percentage, maximum	200.00%
Equity Based Compensation Award Payout Fluctuation Of Award Market	50.00%