Note 6 - Investment Securities (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Available-for-sale Securities	$ 1,227,729,000	$ 1,300,000,000	$ 1,314,345,000	[1]
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	15,400,000	33,500,000
Proceeds From Sales And Repayments Of Other Investment Securities	99,500,000	0
Proceeds from Maturities Repayments and Calls of Other Investment Securities	70,000,000	110,000,000
Realized Loss From Sale And Call Of Investment Securities	438,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	28,000	206,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	12,154,000		14,968,000
Pledged Investment Securities	285,000,000		$ 649,100,000
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	$ 0	$ 0

[1] Preferred stock of government sponsored entities and other equity securities as of December 31, 2015 were reclassified as level 1 rather than level 2 as originally classified due to the availability of quoted prices in active markets.