Note 6 - Investment Securities (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Securities	$ 1,485,124,000		$ 1,586,352,000
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	0	$ 406,900,000
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	33,500,000	12,100,000
Proceeds from Sales and Repayments of Other Investment Securities	0	335,100,000
Proceeds from Maturities Repayments and Calls of Other Investment Securities	110,000,000	0
Realized Loss from Sale and Call of Other Investment Securities	0	1,700,000
Realized Gain from Sale and Call of Other Investment Securities	0	$ 1,700,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	206,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2,875,000		15,923,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	0
Pledged Investment Securities	$ 445,600,000		$ 449,600,000