Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details)

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Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Construction Reserve Funds $ 161,865   $ 161,865   $ 255,408
Exchange Option Liability on Subsidiary Convertible Senior Notes 8,938   8,938   $ 5,611
Marketable security gains (losses), net (8,000) $ (1,700) (56,800) $ (1,300)  
Fair Value, Inputs, Level 1 [Member]          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Marketable securities 78,717   78,717    
Derivative instruments (included in other receivables) 51   51    
Construction Reserve Funds 161,865   161,865    
Short sales of marketable securities 2,745   2,745    
Derivative instruments (included in other current liabilities) 1,479   1,479    
Exchange Option Liability on Subsidiary Convertible Senior Notes 0   0    
Fair Value, Inputs, Level 2 [Member]          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Marketable securities 0   0    
Derivative instruments (included in other receivables) 0   0    
Construction Reserve Funds 0   0    
Short sales of marketable securities 0   0    
Derivative instruments (included in other current liabilities) 481   481    
Exchange Option Liability on Subsidiary Convertible Senior Notes 0   0    
Fair Value, Inputs, Level 3 [Member]          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Marketable securities 0   0    
Derivative instruments (included in other receivables) 0   0    
Construction Reserve Funds 0   0    
Short sales of marketable securities 0   0    
Derivative instruments (included in other current liabilities) 0   0    
Exchange Option Liability on Subsidiary Convertible Senior Notes $ 8,938   $ 8,938