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Note 4 - Fair Value of Financial Instruments Other Fair Value Disclosure (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt $ 1,026,806 $ 1,069,537
Fair Value, Measurements, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets, Fair Value Disclosure 4,570,159 4,461,235
Carrying (Reported) Amount, Fair Value Disclosure [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cost Method Investments 599 1,195
Long-term debt 1,026,806 1,069,537
Estimate of Fair Value, Fair Value Disclosure [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cost Method Investments, Fair Value Disclosure 3,404 3,789
Long-term Debt, Fair Value 1,095,409 1,214,471
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets, Fair Value Disclosure 4,088,954 3,791,284
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets, Fair Value Disclosure $ 0 $ 1,000