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Derivative Financial Instruments (Schedule Of Fair Values Of Derivative Financial Instruments) (Details) (USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2014
Dec. 31, 2013
Derivatives, Fair Value [Line Items]    
Asset Derivatives, Fair Value $ (93,204,000) $ (28,466,000)
Liability Derivatives, Fair Value 37,794,000 4,612,000
Margin deposit asset 130,400,000 77,100,000
Net unrealized losses on cash flow hedges 150,600,000 47,100,000
Derivative Financial Instruments [Member]
    
Derivatives, Fair Value [Line Items]    
Asset Derivatives, Fair Value (93,204,000) [1],[2] (28,466,000) [1],[3]
Accrued And Other Liabilities [Member]
    
Derivatives, Fair Value [Line Items]    
Liability Derivatives, Fair Value $ 37,794,000 $ 4,612,000
[1] Derivative financial instruments as reflected on the consolidated balance sheets are net of related margin deposit assets of $130.4 million and $77.1 million at March 31, 2014 and December 31, 2013, respectively.
[2] Balance at March 31, 2014 includes $150.6 million of net unrealized losses on derivative financial instruments designated as cash flow hedging instruments.
[3] Balance at December 31, 2013 includes $47.1 million of net unrealized losses on derivative financial instruments designated as cash flow hedging instruments.