Note 8 - Investment Securities - Temporarily Impaired Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Temporarily impaired securities, less than 12 months, fair value	$ 845,994	$ 639,985
Temporarily impaired securities, less than 12 months, unrealized losses	49,282	9,198
Temporarily impaired securities, 12 months or longer, fair value	164,771	28,429
Temporarily impaired securities, 12 months or longer, unrealized losses	17,665	1,435
Temporarily impaired securities, total fair value	1,010,765	668,414
Temporarily impaired securities, total unrealized losses	66,947	10,633
US Treasury Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	39,603
Temporarily impaired securities, less than 12 months, unrealized losses	13
Temporarily impaired securities, 12 months or longer, fair value	0
Temporarily impaired securities, 12 months or longer, unrealized losses	0
Temporarily impaired securities, total fair value	39,603
Temporarily impaired securities, total unrealized losses	13
US Government Corporations and Agencies Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	0	0
Temporarily impaired securities, less than 12 months, unrealized losses	0	0
Temporarily impaired securities, 12 months or longer, fair value	2,221	2,337
Temporarily impaired securities, 12 months or longer, unrealized losses	134	135
Temporarily impaired securities, total fair value	2,221	2,337
Temporarily impaired securities, total unrealized losses	134	135
Collateralized Mortgage-Backed Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	695,157	527,276
Temporarily impaired securities, less than 12 months, unrealized losses	40,532	6,659
Temporarily impaired securities, 12 months or longer, fair value	144,040	6,496
Temporarily impaired securities, 12 months or longer, unrealized losses	15,912	755
Temporarily impaired securities, total fair value	839,197	533,772
Temporarily impaired securities, total unrealized losses	56,444	7,414
Collateralized Mortgage Obligations [Member]
Temporarily impaired securities, less than 12 months, fair value	8,274	8,989
Temporarily impaired securities, less than 12 months, unrealized losses	879	417
Temporarily impaired securities, 12 months or longer, fair value	114	128
Temporarily impaired securities, 12 months or longer, unrealized losses	15	13
Temporarily impaired securities, total fair value	8,388	9,117
Temporarily impaired securities, total unrealized losses	894	430
Corporate Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	102,960	103,720
Temporarily impaired securities, less than 12 months, unrealized losses	7,858	2,122
Temporarily impaired securities, 12 months or longer, fair value	18,396	19,468
Temporarily impaired securities, 12 months or longer, unrealized losses	1,604	532
Temporarily impaired securities, total fair value	121,356	123,188
Temporarily impaired securities, total unrealized losses	$ 9,462	$ 2,654

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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