Note 3 - Available for Sale Debt Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available for sale debt securities, amortized cost	$ 1,072,993	$ 574,722
Securities available-for-sale, unrealized gains	7,621	12,785
Securities available-for-sale, unrealized losses	(10,466)	(529)
Securities available-for-sale, fair value	1,070,148	586,978
US Treasury Securities and US Government Agencies Debt Securities [Member]
Available for sale debt securities, amortized cost	83,916
Securities available-for-sale, unrealized gains	0
Securities available-for-sale, unrealized losses	(204)
Securities available-for-sale, fair value	83,712
US Government-sponsored Enterprises Debt Securities [Member]
Available for sale debt securities, amortized cost	142,802	133,436
Securities available-for-sale, unrealized gains	3,553	5,003
Securities available-for-sale, unrealized losses	(68)	(361)
Securities available-for-sale, fair value	146,287	138,078
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available for sale debt securities, amortized cost	777,636	430,198
Securities available-for-sale, unrealized gains	3,784	7,555
Securities available-for-sale, unrealized losses	(9,698)	(168)
Securities available-for-sale, fair value	771,722	437,585
US States and Political Subdivisions Debt Securities [Member]
Available for sale debt securities, amortized cost	67,633	11,088
Securities available-for-sale, unrealized gains	284	227
Securities available-for-sale, unrealized losses	(493)	0
Securities available-for-sale, fair value	67,424	$ 11,315
Other Debt Obligations [Member]
Available for sale debt securities, amortized cost	1,006
Securities available-for-sale, unrealized gains	0
Securities available-for-sale, unrealized losses	(3)
Securities available-for-sale, fair value	$ 1,003

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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