Note 5 - Investment Securities - Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	$ 255,444	$ 269,895
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	6,539	8,777
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	62,932	38,473
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	3,623	2,216
Available for sale securities in a continuous unrealized loss position, fair value	318,376	308,368
Available for sale securities in a continuous unrealized loss position, unrealized losses	10,162	10,993
Held to maturity securities in a continuous unrealized loss position, less than 12 months, fair value	334,304	274,424
Held to maturity securities in a continuous unrealized loss position, less than 12 months, unrealized losses	8,362	7,994
Held to maturity securities in a continuous unrealized loss position, 12 months or more, fair value	23,680	12,158
Held to maturity securities in a continuous unrealized loss position, 12 months or more, unrealized losses	464	124
Held to maturity securities in a continuous unrealized loss position, fair value	357,984	286,582
Held to maturity securities in a continuous unrealized loss position, unrealized losses	8,826	8,118
Collateralized Mortgage Obligations [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	194,126	192,308
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	4,512	5,380
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	7,264	7,579
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	249	252
Available for sale securities in a continuous unrealized loss position, fair value	201,390	199,887
Available for sale securities in a continuous unrealized loss position, unrealized losses	4,761	5,632
Held to maturity securities in a continuous unrealized loss position, less than 12 months, fair value	124,180	108,974
Held to maturity securities in a continuous unrealized loss position, less than 12 months, unrealized losses	2,356	2,469
Held to maturity securities in a continuous unrealized loss position, 12 months or more, fair value	20,325	8,572
Held to maturity securities in a continuous unrealized loss position, 12 months or more, unrealized losses	432	84
Held to maturity securities in a continuous unrealized loss position, fair value	144,505	117,546
Held to maturity securities in a continuous unrealized loss position, unrealized losses	2,788	2,553
US Government Agencies Debt Securities [Member]
Held to maturity securities in a continuous unrealized loss position, less than 12 months, fair value	86,540	67,725
Held to maturity securities in a continuous unrealized loss position, less than 12 months, unrealized losses	2,398	2,198
Held to maturity securities in a continuous unrealized loss position, 12 months or more, fair value	3,355	3,586
Held to maturity securities in a continuous unrealized loss position, 12 months or more, unrealized losses	32	40
Held to maturity securities in a continuous unrealized loss position, fair value	89,895	71,311
Held to maturity securities in a continuous unrealized loss position, unrealized losses	2,430	2,238
Collateralized Mortgage Backed Securities [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	32,174	29,916
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	1,231	1,260
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	2,973	3,199
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	36	35
Available for sale securities in a continuous unrealized loss position, fair value	35,147	33,115
Available for sale securities in a continuous unrealized loss position, unrealized losses	1,267	1,295
Held to maturity securities in a continuous unrealized loss position, less than 12 months, fair value	123,584	97,725
Held to maturity securities in a continuous unrealized loss position, less than 12 months, unrealized losses	3,608	3,327
Held to maturity securities in a continuous unrealized loss position, 12 months or more, fair value
Held to maturity securities in a continuous unrealized loss position, 12 months or more, unrealized losses
Held to maturity securities in a continuous unrealized loss position, fair value	123,584	97,725
Held to maturity securities in a continuous unrealized loss position, unrealized losses	3,608	3,327
US States and Political Subdivisions Debt Securities [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	9,598	15,414
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	342	429
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses
Available for sale securities in a continuous unrealized loss position, fair value	9,598	15,414
Available for sale securities in a continuous unrealized loss position, unrealized losses	342	429
Corporate Debt Securities [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	19,546	32,257
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	454	1,708
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	35,934	10,726
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	2,061	270
Available for sale securities in a continuous unrealized loss position, fair value	55,480	42,983
Available for sale securities in a continuous unrealized loss position, unrealized losses	2,515	1,978
Asset-backed Securities [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	14,800	15,149
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	175	416
Available for sale securities in a continuous unrealized loss position, fair value	14,800	15,149
Available for sale securities in a continuous unrealized loss position, unrealized losses	175	416
Collateralized Debt Obligations [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	1,961	1,820
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	1,102	1,243
Available for sale securities in a continuous unrealized loss position, fair value	1,961	1,820
Available for sale securities in a continuous unrealized loss position, unrealized losses	$ 1,102	$ 1,243