Note 6 - Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
No. of equity securities | security	13	11
Equity Securities in an unrealized loss position less than 12 months, fair value	$ 2,005	$ 2,727
Equity Securities in an unrealized loss position less than 12 months, unrealized losses	(145)	(277)
Equity Securities in an unrealized loss position 12 months or longer, fair value	1,577	275
Equity Securities in an unrealized loss position 12 months or longer, unrealized losses	(455)	(72)
Equity Securities in an unrealized loss position, fair value	3,582	3,002
Equity Securities in an unrealized loss position, unrealized losses	$ (600)	$ (349)
No. of securities | security	386	275
Securities in an unrealized loss position less than 12 months, fair value	$ 82,001	$ 109,879
Securities in an unrealized loss position less than 12 months, unrealized losses	(1,643)	(1,555)
Securities in an unrealized loss position 12 months or longer, fair value	245,524	190,771
Securities in an unrealized loss position 12 months or longer, unrealized losses	(13,109)	(5,611)
Securities in an unrealized loss position, fair value	327,525	300,650
Securities in an unrealized loss position, unrealized losses	$ (14,752)	$ (7,166)
US Government Agencies Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	53	53
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 998	$ 10,828
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(1)	(155)
Debt Securities in an unrealized loss position 12 months or longer, fair value	68,371	59,696
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(3,109)	(1,793)
Debt Securities in an unrealized loss position, fair value	69,369	70,524
Debt Securities in an unrealized loss position, unrealized losses	$ (3,110)	$ (1,948)
US States and Political Subdivisions Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	120	37
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 40,315	$ 10,577
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(680)	(49)
Debt Securities in an unrealized loss position 12 months or longer, fair value	8,964	4,446
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(358)	(64)
Debt Securities in an unrealized loss position, fair value	49,279	15,023
Debt Securities in an unrealized loss position, unrealized losses	$ (1,038)	$ (113)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	113	99
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 21,731	$ 61,069
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(517)	(705)
Debt Securities in an unrealized loss position 12 months or longer, fair value	104,077	72,318
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(5,423)	(1,696)
Debt Securities in an unrealized loss position, fair value	125,808	133,387
Debt Securities in an unrealized loss position, unrealized losses	$ (5,940)	$ (2,401)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	82	70
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 15,961	$ 21,660
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(282)	(349)
Debt Securities in an unrealized loss position 12 months or longer, fair value	59,466	52,833
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(3,690)	(1,943)
Debt Securities in an unrealized loss position, fair value	75,427	74,493
Debt Securities in an unrealized loss position, unrealized losses	$ (3,972)	$ (2,292)
Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	1	1
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 0	$ 0
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	0	0
Debt Securities in an unrealized loss position 12 months or longer, fair value	119	215
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(3)	(26)
Debt Securities in an unrealized loss position, fair value	119	215
Debt Securities in an unrealized loss position, unrealized losses	$ (3)	$ (26)
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	4	4
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 991	$ 3,018
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(18)	(20)
Debt Securities in an unrealized loss position 12 months or longer, fair value	2,950	988
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(71)	(17)
Debt Securities in an unrealized loss position, fair value	3,941	4,006
Debt Securities in an unrealized loss position, unrealized losses	$ (89)	$ (37)