Note 6 - Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
No. of securities | security	361	275
Securities in an unrealized loss position less than 12 months, fair value	$ 126,925	$ 109,879
Securities in an unrealized loss position less than 12 months, unrealized losses	(3,875)	(1,555)
Securities in an unrealized loss position 12 months or longer, fair value	188,344	190,771
Securities in an unrealized loss position 12 months or longer, unrealized losses	(9,503)	(5,611)
Securities in an unrealized loss position, fair value	315,269	300,650
Securities in an unrealized loss position, unrealized losses	$ (13,378)	$ (7,166)
US Government Agencies Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of securities | security	53	53
Securities in an unrealized loss position less than 12 months, fair value	$ 8,731	$ 10,828
Securities in an unrealized loss position less than 12 months, unrealized losses	(258)	(155)
Securities in an unrealized loss position 12 months or longer, fair value	60,764	59,696
Securities in an unrealized loss position 12 months or longer, unrealized losses	(2,724)	(1,793)
Securities in an unrealized loss position, fair value	69,495	70,524
Securities in an unrealized loss position, unrealized losses	$ (2,982)	$ (1,948)
US States and Political Subdivisions Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of securities | security	99	37
Securities in an unrealized loss position less than 12 months, fair value	$ 35,507	$ 10,577
Securities in an unrealized loss position less than 12 months, unrealized losses	(492)	(49)
Securities in an unrealized loss position 12 months or longer, fair value	5,604	4,446
Securities in an unrealized loss position 12 months or longer, unrealized losses	(170)	(64)
Securities in an unrealized loss position, fair value	41,111	15,023
Securities in an unrealized loss position, unrealized losses	$ (662)	$ (113)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of securities | security	108	99
Securities in an unrealized loss position less than 12 months, fair value	$ 53,757	$ 61,069
Securities in an unrealized loss position less than 12 months, unrealized losses	(1,795)	(705)
Securities in an unrealized loss position 12 months or longer, fair value	71,300	72,318
Securities in an unrealized loss position 12 months or longer, unrealized losses	(3,419)	(1,696)
Securities in an unrealized loss position, fair value	125,057	133,387
Securities in an unrealized loss position, unrealized losses	$ (5,214)	$ (2,401)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of securities | security	77	70
Securities in an unrealized loss position less than 12 months, fair value	$ 21,839	$ 21,660
Securities in an unrealized loss position less than 12 months, unrealized losses	(712)	(349)
Securities in an unrealized loss position 12 months or longer, fair value	48,757	52,833
Securities in an unrealized loss position 12 months or longer, unrealized losses	(2,813)	(1,943)
Securities in an unrealized loss position, fair value	70,596	74,493
Securities in an unrealized loss position, unrealized losses	$ (3,525)	$ (2,292)
Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of securities | security	1	1
Securities in an unrealized loss position less than 12 months, fair value	$ 0	$ 0
Securities in an unrealized loss position less than 12 months, unrealized losses	0	0
Securities in an unrealized loss position 12 months or longer, fair value	118	215
Securities in an unrealized loss position 12 months or longer, unrealized losses	(5)	(26)
Securities in an unrealized loss position, fair value	118	215
Securities in an unrealized loss position, unrealized losses	$ (5)	$ (26)
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of securities | security	4	4
Securities in an unrealized loss position less than 12 months, fair value	$ 2,963	$ 3,018
Securities in an unrealized loss position less than 12 months, unrealized losses	(68)	(20)
Securities in an unrealized loss position 12 months or longer, fair value	969	988
Securities in an unrealized loss position 12 months or longer, unrealized losses	(35)	(17)
Securities in an unrealized loss position, fair value	3,932	4,006
Securities in an unrealized loss position, unrealized losses	$ (103)	$ (37)
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of securities | security	19	11
Securities in an unrealized loss position less than 12 months, fair value	$ 4,128	$ 2,727
Securities in an unrealized loss position less than 12 months, unrealized losses	(550)	(277)
Securities in an unrealized loss position 12 months or longer, fair value	832	275
Securities in an unrealized loss position 12 months or longer, unrealized losses	(337)	(72)
Securities in an unrealized loss position, fair value	4,960	3,002
Securities in an unrealized loss position, unrealized losses	$ (887)	$ (349)