Quarterly report pursuant to Section 13 or 15(d)

Note 10 - Fair Value Measurement - Financial Assets and Financial Liabilities Carried at Fair Value on a Recurring Basis (Details)

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Note 10 - Fair Value Measurement - Financial Assets and Financial Liabilities Carried at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Available-for-sale securities $ 435,325 $ 422,375
US Treasury and Government [Member]    
Available-for-sale securities 56,778 46,254
Collateralized Mortgage Backed Securities [Member]    
Available-for-sale securities 243,743 227,190
US States and Political Subdivisions Debt Securities [Member]    
Available-for-sale securities 134,804 139,930
Corporate Debt Securities [Member]    
Available-for-sale securities   9,001
Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities 435,325 422,375
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Available-for-sale securities 56,778 46,254
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]    
Available-for-sale securities 243,743 227,190
Fair Value, Measurements, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available-for-sale securities 134,804 139,930
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Available-for-sale securities   9,001
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]    
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]    
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Backed Securities [Member]    
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]    
Available-for-sale securities  
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]    
Available-for-sale securities 435,325 422,375
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]    
Available-for-sale securities 56,778 46,254
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Backed Securities [Member]    
Available-for-sale securities 243,743 227,190
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available-for-sale securities 134,804 139,930
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]    
Available-for-sale securities   9,001
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]    
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]    
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Collateralized Mortgage Backed Securities [Member]    
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]    
Available-for-sale securities