Note 6 - Investment Securities (Details) - Investment Securities - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Securities Available-for-Sale
Securities available-for-sale, amortized cost	$ 1,476,424	$ 1,595,723
Securities available-for-sale, gross unrealized gains	11,575	6,552
Securities available-for-sale, gross unrealized losses	2,875	15,923
Securities available-for-sale	1,485,124	1,586,352
US Treasury Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	224,750	284,678
Securities available-for-sale, gross unrealized gains	61	5
Securities available-for-sale, gross unrealized losses	7	395
Securities available-for-sale	224,804	284,288
US Government-sponsored Enterprises Debt Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	100,000	150,000
Securities available-for-sale, gross unrealized gains	10
Securities available-for-sale, gross unrealized losses		1,840
Securities available-for-sale	100,010	148,160
Collateralized Mortgage Backed Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	1,063,944	1,073,108
Securities available-for-sale, gross unrealized gains	6,553	560
Securities available-for-sale, gross unrealized losses	4	11,399
Securities available-for-sale	1,070,493	1,062,269
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	60	63
Securities available-for-sale, gross unrealized losses	26	27
Securities available-for-sale	34	36
Corporate Debt Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	74,957	74,955
Securities available-for-sale, gross unrealized gains	413	425
Securities available-for-sale, gross unrealized losses	2,267	1,525
Securities available-for-sale	73,103	73,855
Mutual Funds [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	6,000	6,000
Securities available-for-sale, gross unrealized losses	85	167
Securities available-for-sale	5,915	5,833
Preferred Stock of Government Sponsored Entities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	2,811	2,811
Securities available-for-sale, gross unrealized gains	478	633
Securities available-for-sale, gross unrealized losses	486	228
Securities available-for-sale	2,803	3,216
Other Equity Securities [Member]
Securities Available-for-Sale
Securities available-for-sale, amortized cost	3,902	4,108
Securities available-for-sale, gross unrealized gains	4,060	4,929
Securities available-for-sale, gross unrealized losses		342
Securities available-for-sale	$ 7,962	$ 8,695