Note 6 - Investment Securities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Securities	$ 1,545,699		$ 1,318,935
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	573,500	$ 386,500
Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS)	36,500	39,600
Proceeds from Sales and Repayments of Other Investment Securities	385,200	80,400
Proceeds from Maturities Repayments and Calls of Other Investment Securities	0	135,800
Realized Gain from Sale and Call of Investment Securities	2,300	12,800
Realized Loss from Sale and Call of Investment Securities	1,800	$ 6,300
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	10,920		11,799
Pledged Investment Securities	$ 519,200		$ 591,300