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, 2019
Dec. 31, 2018
3.0% Convertible Senior Notes    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt instrument, stated percentage 3.00%  
3.25% Convertible Senior Notes    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt instrument, stated percentage 3.25%  
Convertible Debt | 3.0% Convertible Senior Notes    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt instrument, stated percentage 3.00%  
Convertible Debt | 3.25% Convertible Senior Notes    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt instrument, stated percentage 3.25%  
Reported Value Measurement    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable from third parties (included in other receivables and other assets) $ 1,119 $ 2,182
Investments, at cost, in 50% or less owned companies (included in other assets) 4,201 4,300
Long-term debt, including current portion 314,466 354,625
Estimate of Fair Value Measurement | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable from third parties (included in other receivables and other assets) 0 0
Long-term debt, including current portion 0 0
Estimate of Fair Value Measurement | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable from third parties (included in other receivables and other assets) 1,082 2,159
Long-term debt, including current portion 330,088 353,929
Estimate of Fair Value Measurement | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable from third parties (included in other receivables and other assets) 0 0
Long-term debt, including current portion $ 0 $ 0