Quarterly report pursuant to Section 13 or 15(d)

Note 11 - Fair Value Measurement (Details Textual)

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Note 11 - Fair Value Measurement (Details Textual)
3 Months Ended 12 Months Ended
Mar. 31, 2020
USD ($)
Mar. 31, 2019
USD ($)
Dec. 31, 2019
USD ($)
Debt Securities, Available-for-sale, Total $ 826,782,000   $ 759,399,000 [1]
Asset Impairment Charges, Total 5,000,000.0 $ 1,900,000  
Real Estate Owned, Amount of Loss at Acquisition 563,000 $ 22,000  
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Foreclosure 287,000   103,000
Mortgage Loans in Process of Foreclosure, Amount 600,000   287,000
Liabilities, Total 8,482,997,000   8,104,971,000 [1]
Fair Value, Recurring [Member]      
Debt Securities, Available-for-sale, Total 826,782,000   759,399,000
Liabilities, Total 0   0
Fair Value, Nonrecurring [Member]      
Liabilities, Total $ 0   $ 0
Minimum [Member]      
Impaired Loans, Fair Value Adjustment, Percent 0.00%   0.00%
Real Estate Owned, Fair Value Adjustment, Percent 5.00%   5.00%
Weighted Average [Member]      
Impaired Loans, Fair Value Adjustment, Percent 16.60%   5.60%
Real Estate Owned, Fair Value Adjustment, Percent 7.80%   8.00%
Maximum [Member]      
Impaired Loans, Fair Value Adjustment, Percent 50.00%   30.00%
Real Estate Owned, Fair Value Adjustment, Percent 10.00%   10.00%
Corporate Debt Securities [Member]      
Number of Available-for-sale Debt Securities Acquired 2    
Debt Securities, Available-for-sale, Total $ 160,648,000   $ 160,477,000
Corporate Debt Securities [Member] | Fair Value, Recurring [Member]      
Debt Securities, Available-for-sale, Total 160,648,000   160,477,000
Corporate Debt Securities [Member] | Minimum [Member]      
Debt Securities, Available-for-sale, Total 94,574,400   98,783,600
Corporate Debt Securities [Member] | Weighted Average [Member]      
Debt Securities, Available-for-sale, Total 106,777,500   112,230,500
Corporate Debt Securities [Member] | Maximum [Member]      
Debt Securities, Available-for-sale, Total $ 102,386,500   $ 102,264,800
[1] derived from audited financial statements.