Note 6 - Investment Securities (Details Textual) - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Proceeds From Sales And Repayments Of Other Investment Securities	$ 0	$ 385,200,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	0
Available-for-sale Securities	1,298,469,000		$ 1,586,352,000
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	415,300,000	648,000,000
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	125,300,000	67,300,000
Proceeds from Maturities Repayments and Calls of Other Investment Securities	460,000,000	165,000,000
Realized Gain From Sale And Call Of Investment Securities	3,300,000	2,400,000
Realized Loss From Sale And Call Of Investment Securities	0	$ 1,900,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	206,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,316,000		15,923,000
Pledged Investment Securities	$ 505,900,000		$ 449,600,000