Note 7 - Investment Securities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Securities	$ 1,380,879		$ 1,318,935
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	648,000	$ 458,400
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	67,300	54,700
Proceeds from Sales and Repayments of Other Investment Securities	385,200	84,900
Proceeds from Maturities Repayments and Calls of Other Investment Securities	165,000	585,800
Realized Gain from Sale and Call of Investment Securities	2,400	17,100
Realized Loss from Sale and Call of Investment Securities	1,900	$ 9,500
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	4,142		11,799
Pledged Investment Securities	$ 457,000		$ 591,300