Note 4 - Debt and Equity Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Details) $ in Thousands	Sep. 30, 2020 USD ($) item	Dec. 31, 2019 USD ($)
Available-for-Sale Securities, Less than 12 Months, Fair Value	$ 135,194	$ 110,599
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 1,005	$ 1,240
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	56	62
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 11,585	$ 92,750
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 166	$ 730
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	13	75
Available-for-Sale Securities, Total, Fair Value	$ 146,779	$ 203,349
Available-for-Sale Securities, Total, Unrealized Losses	1,171	1,970
US Government-sponsored Enterprises Debt Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	37,470	16,507
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 78	$ 114
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	14	5
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 0	$ 24,658
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 90
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	0	9
Available-for-Sale Securities, Total, Fair Value	$ 37,470	$ 41,165
Available-for-Sale Securities, Total, Unrealized Losses	78	204
Collateralized Mortgage Backed Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	66,980	45,862
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 586	$ 182
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	23	21
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 2,096	$ 56,917
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 21	$ 453
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	11	52
Available-for-Sale Securities, Total, Fair Value	$ 69,076	$ 102,779
Available-for-Sale Securities, Total, Unrealized Losses	607	635
Asset-backed Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	564	17,807
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 6	$ 161
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	1	10
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 8,792	$ 7,317
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 127	$ 142
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	1	4
Available-for-Sale Securities, Total, Fair Value	$ 9,356	$ 25,124
Available-for-Sale Securities, Total, Unrealized Losses	133	303
Corporate Debt Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	0	0
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 0	$ 0
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	0	0
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	0	0
Available-for-Sale Securities, Total, Fair Value	$ 0	$ 0
Available-for-Sale Securities, Total, Unrealized Losses	0	0
US States and Political Subdivisions Debt Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	30,180	30,423
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 335	$ 783
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	18	26
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 697	$ 3,858
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 18	$ 45
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	1	10
Available-for-Sale Securities, Total, Fair Value	$ 30,877	$ 34,281
Available-for-Sale Securities, Total, Unrealized Losses	$ 353	$ 828

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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