Note 6 - Investment Securities (Details) - Investment Securities - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Securities Available-for-Sale
Securities available-for-sale, amortized cost	$ 1,547,642	$ 1,324,408
Securities available-for-sale, gross unrealized gains	8,977	6,326
Securities available-for-sale, gross unrealized losses	10,920	11,799
Securities available-for-sale	1,545,699	1,318,935
US Treasury Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	299,911	664,206
Securities available-for-sale, gross unrealized gains	199	63
Securities available-for-sale, gross unrealized losses		265
Securities available-for-sale	300,110	664,004
US Government-sponsored Enterprises Debt Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	49,975
Securities available-for-sale, gross unrealized gains	152
Securities available-for-sale	50,127
Collateralized Mortgage Backed Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	1,110,298	549,296
Securities available-for-sale, gross unrealized gains	759	1,393
Securities available-for-sale, gross unrealized losses	9,654	6,386
Securities available-for-sale	1,101,403	544,303
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	70	79
Securities available-for-sale, gross unrealized losses	30	34
Securities available-for-sale	40	45
Corporate Debt Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	74,949	94,943
Securities available-for-sale, gross unrealized gains	528	776
Securities available-for-sale, gross unrealized losses	1,078	1,247
Securities available-for-sale	74,399	94,472
Mutual Funds [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	6,000	6,000
Securities available-for-sale, gross unrealized losses	156	134
Securities available-for-sale	5,844	5,866
Preferred Stock of Government Sponsored Entities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	2,811	6,276
Securities available-for-sale, gross unrealized gains	733	681
Securities available-for-sale, gross unrealized losses		3,733
Securities available-for-sale	3,544	3,224
Other Equity Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	3,628	3,608
Securities available-for-sale, gross unrealized gains	6,606	3,413
Securities available-for-sale, gross unrealized losses	2
Securities available-for-sale	$ 10,232	$ 7,021