Note 2 - Securities - Amortized Cost and Fair Value of Investments in Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Securities available for sale, amortized cost	$ 640,507	$ 455,992
Securities available for sale, unrealized gains	6,907	10,261
Securities available for sale, unrealized losses	3,465	162
Securities available for sale, fair value	643,949	466,091
US Treasury Securities [Member]
Securities available for sale, amortized cost	110,154	34,997
Securities available for sale, unrealized gains	92	1
Securities available for sale, unrealized losses	205	0
Securities available for sale, fair value	110,041	34,998
US Government-sponsored Enterprises Debt Securities [Member]
Securities available for sale, amortized cost	89,680	104,092
Securities available for sale, unrealized gains	1,298	1,976
Securities available for sale, unrealized losses	482	45
Securities available for sale, fair value	90,496	106,023
Collateralized Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	358,910	246,770
Securities available for sale, unrealized gains	3,933	6,117
Securities available for sale, unrealized losses	2,436	105
Securities available for sale, fair value	360,407	252,782
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale, amortized cost	62,813	57,122
Securities available for sale, unrealized gains	1,336	1,979
Securities available for sale, unrealized losses	282	2
Securities available for sale, fair value	63,867	59,099
Corporate Debt Securities [Member]
Securities available for sale, amortized cost	18,950	13,011
Securities available for sale, unrealized gains	248	188
Securities available for sale, unrealized losses	60	10
Securities available for sale, fair value	$ 19,138	$ 13,189

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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