Quarterly report pursuant to Section 13 or 15(d)

Note 11 - Fair Value Measurement - Financial Assets and Financial Liabilities Carried at Fair Value on a Recurring Basis (Details)

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Note 11 - Fair Value Measurement - Financial Assets and Financial Liabilities Carried at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Available-for-sale securities $ 631,696 $ 590,184 [1]
US Treasury and Government [Member]    
Available-for-sale securities 74,081 76,993
Collateralized Mortgage Backed Securities [Member]    
Available-for-sale securities 329,376 304,304
US States and Political Subdivisions Debt Securities [Member]    
Available-for-sale securities 96,468 105,994
Corporate Debt Securities [Member]    
Available-for-sale securities 131,771 102,893
Fair Value, Recurring [Member]    
Available-for-sale securities
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]    
Available-for-sale securities 625,193 583,666
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]    
Available-for-sale securities 6,503 6,518
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]    
Available-for-sale securities 631,696 590,184
Fair Value, Recurring [Member] | US Treasury and Government [Member]    
Available-for-sale securities
Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]    
Available-for-sale securities 74,081 76,993
Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]    
Available-for-sale securities
Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]    
Available-for-sale securities 74,081 76,993
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]    
Available-for-sale securities
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]    
Available-for-sale securities 329,376 304,304
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]    
Available-for-sale securities
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]    
Available-for-sale securities 329,376 304,304
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]    
Available-for-sale securities
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]    
Available-for-sale securities 96,468 105,994
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]    
Available-for-sale securities
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]    
Available-for-sale securities 96,468 105,994
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]    
Available-for-sale securities
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]    
Available-for-sale securities 125,268 96,375
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]    
Available-for-sale securities 6,503 6,518
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]    
Available-for-sale securities $ 131,771 $ 102,893
[1] Derived from audited financial statements.