Note 3 - Available for Sale Debt Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Available for sale debt securities, amortized cost	$ 1,003,871	$ 574,722
Securities available-for-sale, unrealized gains	9,408	12,785
Securities available-for-sale, unrealized losses	(6,371)	(529)
Securities available-for-sale, fair value	1,006,908	586,978
US Treasury Securities and US Government Agencies Debt Securities [Member]
Available for sale debt securities, amortized cost	9,078
Securities available-for-sale, unrealized gains	0
Securities available-for-sale, unrealized losses	(1)
Securities available-for-sale, fair value	9,077
US Government-sponsored Enterprises Debt Securities [Member]
Available for sale debt securities, amortized cost	150,833	133,436
Securities available-for-sale, unrealized gains	4,271	5,003
Securities available-for-sale, unrealized losses	(124)	(361)
Securities available-for-sale, fair value	154,980	138,078
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available for sale debt securities, amortized cost	788,048	430,198
Securities available-for-sale, unrealized gains	4,781	7,555
Securities available-for-sale, unrealized losses	(6,118)	(168)
Securities available-for-sale, fair value	786,711	437,585
US States and Political Subdivisions Debt Securities [Member]
Available for sale debt securities, amortized cost	54,906	11,088
Securities available-for-sale, unrealized gains	355	227
Securities available-for-sale, unrealized losses	(128)	0
Securities available-for-sale, fair value	55,133	$ 11,315
Other Debt Obligations [Member]
Available for sale debt securities, amortized cost	1,006
Securities available-for-sale, unrealized gains	1
Securities available-for-sale, unrealized losses	0
Securities available-for-sale, fair value	$ 1,007

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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