Note 6 - Investment Securities (Details Textual) - USD ($)	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Available-for-sale Securities	$ 1,241,904,000		$ 1,586,352,000
Proceeds From Sales And Repayments Of Other Investment Securities	0	$ 385,200,000
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	241,800,000	573,500,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	0
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	80,700,000	36,500,000
Proceeds from Maturities Repayments and Calls of Other Investment Securities	335,000,000	0
Realized Gain From Sale And Call Of Investment Securities	1,700,000	2,300,000
Realized Loss From Sale And Call Of Investment Securities	0	$ 1,800,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	206,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,856,000		15,923,000
Pledged Investment Securities	$ 471,600,000		$ 449,600,000