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
Mar. 31, 2018
Dec. 31, 2017
Available for sale debt securities $ 560,635 $ 538,080 [1]
Fair Value, Measurements, Recurring [Member]    
Available for sale debt securities 560,635 538,080
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Available for sale debt securities 57,252 55,356
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]    
Available for sale debt securities 288,318 276,498
Fair Value, Measurements, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available for sale debt securities 122,789 134,849
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Available for sale debt securities 92,276 71,377
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]    
Available for sale debt securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]    
Available for sale debt securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Backed Securities [Member]    
Available for sale debt securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available for sale debt securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]    
Available for sale debt securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]    
Available for sale debt securities 554,032 531,580
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]    
Available for sale debt securities 57,252 55,356
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Backed Securities [Member]    
Available for sale debt securities 288,318 276,498
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available for sale debt securities 122,789 134,849
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]    
Available for sale debt securities 85,673 64,877
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]    
Available for sale debt securities 6,603 6,500
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]    
Available for sale debt securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Collateralized Mortgage Backed Securities [Member]    
Available for sale debt securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available for sale debt securities
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]    
Available for sale debt securities $ 6,603 $ 6,500
[1] derived from audited financial statements