Annual report pursuant to Section 13 and 15(d)

Nature Of Operations And Accounting Policies (Schedule Of Deferred Gain Activity) (Details)

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Nature Of Operations And Accounting Policies (Schedule Of Deferred Gain Activity) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Jan. 01, 2019
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]        
Amortization of deferred gains included in operating expenses as a reduction to rental expense $ 0 $ 0 $ 12,774  
Operating Expense        
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]        
Amortization of deferred gains included in operating expenses as a reduction to rental expense 0 0 12,774  
Gains on Asset Dispositions and Impairments, Net        
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]        
Amortization of deferred gains included in gains on asset dispositions, net 0 (1,127) (11,591)  
Amortization of deferred gains included in gains on asset dispositions, net (1,322) (1,322) (1,372)  
Sale Leaseback and Financed Equipment Sales        
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]        
Balance at beginning of year 8,768 39,102 66,519  
Reclassification of deferred gains into historical cost on reacquired property and equipment 0 0 (3,052)  
Balance at end of year 8,768 8,768 39,102  
Fifty Percent or Less Owned Subsidiaries        
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]        
Balance at beginning of year 3,240 4,562 5,934  
Balance at end of year 1,918 $ 3,240 $ 4,562  
Sale Leaseback | Retained Earnings | Accounting Standards Update 2016-02        
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]        
Impact of adoption of accounting principle $ 0     $ 29,207