Note 3 - Investment Securities Available-for-sale - Securities Available-for-sale by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized cost	$ 502,403	$ 541,364
Estimated fair value	499,807	538,108
US Government Agencies Debt Securities [Member]
One year or less, amortized cost	82,631	83,885
One year or less, estimated fair value	81,401	82,548
After one year through five years, amortized cost	47,693	20,736
After one year through five years, estimated fair value	47,725	20,897
Five years through ten years, amortized cost	9,071	2,804
Five years through ten years, estimated fair value	9,017	2,697
After ten years, amortized cost	9,765
After ten years, estimated fair value	9,765
After ten years, estimated fair value	9,765
Residential Mortgage Backed Securities [Member]
Amortized cost, without maturity date	299,757	329,606
Estimated fair value, without maturity date	296,925	326,239
US States and Political Subdivisions Debt Securities [Member]
One year or less, amortized cost	831	1,056
One year or less, estimated fair value	837	1,070
After one year through five years, amortized cost	19,913	45,808
After one year through five years, estimated fair value	20,801	46,865
Five years through ten years, amortized cost	21,437	46,668
Five years through ten years, estimated fair value	21,794	46,839
After ten years, amortized cost	1,074	1,075
After ten years, estimated fair value	1,177	1,156
After ten years, estimated fair value	1,177	1,156
Corporate Debt Securities [Member]
After one year through five years, amortized cost	8,513	8,008
After one year through five years, estimated fair value	8,647	8,079
After ten years, amortized cost	1,500	1,500
After ten years, estimated fair value	1,500	1,500
After ten years, estimated fair value	1,500	1,500
Equity Investment Other [Member]
Amortized cost, without maturity date	218	218
Estimated fair value, without maturity date	$ 218	$ 218