Note 7 - Investment Securities (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale, Total	$ 1,241,105,000	$ 1,300,000,000		$ 1,333,626,000
Proceeds from Sale of Mortgage-backed Securities (MBS), Available-for-sale	0	0
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	22,900,000	15,400,000
Proceeds From Sales And Repayments Of Other Investment Securities	0	99,500,000
Proceeds from Maturities Repayments and Calls of Other Investment Securities	151,000,000	70,000,000
Realized Loss From Sale And Call Of Investment Securities	0	438,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Total	0	28,000
Equity Securities, FV-NI, Unrealized Gain (Loss), Total	(3,847,000)
Equity Securities, FV-NI	24,154,000			28,100,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss, Total	31,700,000			16,684,000
Pledged Investment Securities	$ 231,000,000			$ 272,200,000
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ 8,600,000