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
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Construction Reserve Funds & Title XI Reserve Funds $ 275,131   $ 278,022
Marketable security gains (losses), net 6,000 $ 2,100  
Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities 29,411    
Derivative instruments (included in other receivables) 472    
Construction Reserve Funds & Title XI Reserve Funds 275,131    
Short sales of marketable securities 9,155    
Derivative instruments (included in other current liabilities) 2,048    
Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities 0    
Derivative instruments (included in other receivables) 259    
Construction Reserve Funds & Title XI Reserve Funds 0    
Short sales of marketable securities 0    
Derivative instruments (included in other current liabilities) 423    
Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities 0    
Derivative instruments (included in other receivables) 0    
Construction Reserve Funds & Title XI Reserve Funds 0    
Short sales of marketable securities 0    
Derivative instruments (included in other current liabilities) $ 0