Note 6 - Investment Securities (Details Textual) - USD ($)	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Available-for-sale Securities	$ 1,368,351,000		$ 1,314,345,000	[1]
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	0	$ 241,800,000
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	28,600,000	80,700,000
Proceeds From Sales And Repayments Of Other Investment Securities	99,500,000	0
Proceeds from Maturities Repayments and Calls of Other Investment Securities	170,000,000	335,000,000
Realized Loss From Sale And Call Of Investment Securities	438,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	25,000	$ 206,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	8,717,000		14,968,000
Pledged Investment Securities	$ 225,600,000		$ 649,100,000

[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.