Note 3 - Debt and Equity Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Details) $ in Thousands	Jun. 30, 2021 USD ($) item	Dec. 31, 2020 USD ($) item
Available-for-Sale Securities, Less than 12 Months, Fair Value	$ 390,322	$ 175,383
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 6,182	$ 1,121
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	182	83
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 12,365	$ 7,465
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 44	$ 53
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	14	13
Available-for-Sale Securities, Total, Fair Value	$ 402,687	$ 182,848
Available-for-Sale Securities, Total, Unrealized Losses	6,226	1,174
US Treasury and Other US Government Agencies Debt Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	4,921	0
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 18	$ 0
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	2	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	$ 4,921	$ 0
Available-for-Sale Securities, Total, Unrealized Losses	18	0
US Government-sponsored Enterprises Debt Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	108,607	47,991
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 2,140	$ 135
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	41	18
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	$ 108,607	$ 47,991
Available-for-Sale Securities, Total, Unrealized Losses	2,140	135
Collateralized Mortgage Backed Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	201,469	78,381
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 2,405	$ 573
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	68	29
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 12,365	$ 6,776
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 44	$ 47
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	14	12
Available-for-Sale Securities, Total, Fair Value	$ 213,834	$ 85,157
Available-for-Sale Securities, Total, Unrealized Losses	2,449	620
Asset-backed Securities [Member]
Available-for-Sale Securities, Less than 12 Months, Fair Value	507	4,950
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 14	$ 19
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	1	3
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	$ 507	$ 4,950
Available-for-Sale Securities, Total, Unrealized Losses	14	19
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 \| item	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 \| item	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	74,818	44,061
Available-for-Sale Securities, Less than 12 Months, Unrealized Losses	$ 1,605	$ 394
Available-for-Sale Securities, Less than 12 Months, Number of Securities Included	70	33
Available-for-Sale Securities, 12 Months or More, Fair Value	$ 0	$ 689
Available-for-Sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 6
Available-for-Sale Securities, 12 Months or More, Number of Securities Included	0	1
Available-for-Sale Securities, Total, Fair Value	$ 74,818	$ 44,750
Available-for-Sale Securities, Total, Unrealized Losses	$ 1,605	$ 400

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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