Note 3 - Investment Securities (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Proceeds from Sale of Debt Securities, Available-for-sale	$ 293,800	$ 99,900
Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale	296,721	447,773	$ 562,595
Debt Securities, Available-for-sale, Realized Gain	583,000	36,000
Debt Securities, Available-for-sale, Realized Loss	$ 372,000	14,000
Temporarily Impaired Securities As Percentage Of Investment Securities	34.00%
Percentage Of Unrealized Losses For Securities With Unrealized Losses For Less Than Twelve Months	0.20%
Percentage Of Unrealized Losses For Securities With Unrealized Losses For Greater Than Twelve Months	0.40%
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 1,740	27,000
Pledged Investment Securities	20,100	28,500
Equity Securities, FV-NI, Unrealized Gain (Loss), Total	5,736	(2,787)	$ (0)
Equity Securities, FV-NI	$ 28,005	25,098
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 8,600