Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements Fair Value Measurements (Estimated Fair Value of Other Financial Assets and Liabilities) (Details)

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Fair Value Measurements Fair Value Measurements (Estimated Fair Value of Other Financial Assets and Liabilities) (Details)
$ in Thousands
Sep. 30, 2019
USD ($)
3.0% Convertible Senior Notes  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt instrument, interest rate, stated percentage 3.00%
3.25% Convertible Senior Notes  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt instrument, interest rate, stated percentage 3.25%
Convertible Debt | 3.0% Convertible Senior Notes  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt instrument, interest rate, stated percentage 3.00%
Convertible Debt | Two Point Five Percentage Convertible Notes  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt instrument, interest rate, stated percentage 2.50%
Convertible Debt | 3.25% Convertible Senior Notes  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt instrument, interest rate, 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) $ 1,112
Investments, at cost, in 50% or less owned companies (included in other assets) 4,300
Long-term debt, including current portion 317,834
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
Long-term debt, including current portion 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) 1,112
Long-term debt, including current portion 334,623
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
Long-term debt, including current portion $ 0