Note 4 - Investment Securities (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Investments, Debt and Equity Securities [Abstract]
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	$ 648,000,000	$ 698,500,000
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	101,200,000	69,700,000
Proceeds from Sales and Repayments of Other Investment Securities	385,200,000	160,500,000
Proceeds from Maturities Repayments and Calls of Other Investment Securities	165,000,000	585,800,000
Realized Gain from Sale and Call of Other Investment Securities	2,400,000	18,000,000
Realized Loss from Sale and Call of Other Investment Securities	1,900,000	10,500,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	$ 3,900,000	$ 800,000
Temporarily Impaired Securities As Percentage of Investment Securities	92.00%
Percentage of Unrealized Losses for Securities with Unrealized Losses for Less Than Twelve Months	1.00%
Percentage of Unrealized Losses for Securities with Unrealized Losses for Greater than Twelve Months	3.30%
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	7	22
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	47	8
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 15,923,000	$ 11,799,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	0
Pledged Investment Securities	$ 449,600,000	$ 591,300,000