Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Estimated Fair Value Of Other Financial Assets And Liabilities) (Details)

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Fair Value Measurements (Estimated Fair Value Of Other Financial Assets And Liabilities) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Nov. 13, 2013
Dec. 11, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Investment Owned, at Cost $ 4,300 $ 4,300    
Notes, Loans and Financing Receivable, Gross, Noncurrent 2,647 12,342    
Debt, Long-term and Short-term, Combined Amount 579,347 794,286    
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents $ 242,228 $ 258,887    
Two Point Five Percentage Convertible Notes [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt Instrument, Interest Rate, Stated Percentage 2.50% 2.50%   2.50%
Three Point Zero Percentage Convertible Notes [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt Instrument, Interest Rate, Stated Percentage 3.00%   3.00%  
Fair Value, Inputs, Level 1 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Cash and Cash Equivalents, Fair Value Disclosure $ 242,228 $ 258,887    
Notes Receivable, Fair Value Disclosure 943 10,000    
Long-term Debt, Fair Value 0 0    
Fair Value, Inputs, Level 2 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Cash and Cash Equivalents, Fair Value Disclosure 0 0    
Notes Receivable, Fair Value Disclosure 1,642 2,206    
Long-term Debt, Fair Value 596,246 819,756    
Fair Value, Inputs, Level 3 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Cash and Cash Equivalents, Fair Value Disclosure 0 0    
Notes Receivable, Fair Value Disclosure 0 0    
Long-term Debt, Fair Value $ 0 $ 0