Note 6 - Investment Securities - Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Securities available-for-sale, gross unrealized gains	$ 10,444	$ 12,301
Securities available-for-sale, gross unrealized losses	8,717	14,968
Securities available-for-sale	1,368,351	1,314,345	[1]
Securities available-for-sale, amortized cost	1,366,624	1,317,012
US Treasury Securities [Member]
Securities available-for-sale, gross unrealized gains		35
Securities available-for-sale, gross unrealized losses	524	857
Securities available-for-sale	569,045	489,017
Securities available-for-sale, amortized cost	569,569	489,839
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, gross unrealized gains
Securities available-for-sale, gross unrealized losses	5,369	9,669
Securities available-for-sale	394,631	390,331
Securities available-for-sale, amortized cost	400,000	400,000
Collateralized Mortgage Backed Securities [Member]
Securities available-for-sale, gross unrealized gains	221	309
Securities available-for-sale, gross unrealized losses	2,480	3,290
Securities available-for-sale	306,907	336,260
Securities available-for-sale, amortized cost	309,166	339,241
Corporate Debt Securities [Member]
Securities available-for-sale, gross unrealized gains	549	247
Securities available-for-sale, gross unrealized losses	109	862
Securities available-for-sale	75,410	74,350
Securities available-for-sale, amortized cost	74,970	74,965
Collateralized Mortgage Obligations [Member]
Securities available-for-sale, gross unrealized gains
Securities available-for-sale, gross unrealized losses		20
Securities available-for-sale		28
Securities available-for-sale, amortized cost		48
Mutual Funds [Member]
Securities available-for-sale, gross unrealized gains
Securities available-for-sale, gross unrealized losses	235	270
Securities available-for-sale	6,265	6,230
Securities available-for-sale, amortized cost	6,500	6,500
Preferred Stock of Government Sponsored Entities [Member]
Securities available-for-sale, gross unrealized gains	2,413	4,497
Securities available-for-sale, gross unrealized losses
Securities available-for-sale	5,224	7,308	[2]
Securities available-for-sale, amortized cost	2,811	2,811
Other Equity Securities [Member]
Securities available-for-sale, gross unrealized gains	7,261	7,213
Securities available-for-sale, gross unrealized losses
Securities available-for-sale	10,869	10,821	[2]
Securities available-for-sale, amortized cost	$ 3,608	$ 3,608

[1] Preferred stock of government sponsored entities and other equity securities as of December 31, 2015 were reclassified as level 1 rather than level 2 as originally classified due to the availability of quoted prices in active markets.

[2] Preferred stock of government sponsored entities and other equity securities as of December 31, 2015 were reclassified as level 1 rather than level 2 as originally classified due to the availability of quoted prices in active markets.