Note 6 - Debt Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	252	321
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 4,435	$ 34,651
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(5)	(296)
Debt Securities in an unrealized loss position 12 months or longer, fair value	251,077	254,299
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(5,418)	(9,126)
Debt Securities in an unrealized loss position, fair value	255,512	288,950
Debt Securities in an unrealized loss position, unrealized losses	$ (5,423)	$ (9,422)
US Government Agencies Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	51	51
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	69,359	68,409
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(1,123)	(2,072)
Debt Securities in an unrealized loss position, fair value	69,359	68,409
Debt Securities in an unrealized loss position, unrealized losses	$ (1,123)	$ (2,072)
US States and Political Subdivisions Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	21	81
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 569	$ 21,657
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(1)	(204)
Debt Securities in an unrealized loss position 12 months or longer, fair value	7,493	10,558
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(60)	(260)
Debt Securities in an unrealized loss position, fair value	8,062	32,215
Debt Securities in an unrealized loss position, unrealized losses	$ (61)	$ (464)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	102	111
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 3,573	$ 12,561
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(4)	(91)
Debt Securities in an unrealized loss position 12 months or longer, fair value	109,299	108,802
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(2,407)	(4,160)
Debt Securities in an unrealized loss position, fair value	112,872	121,363
Debt Securities in an unrealized loss position, unrealized losses	$ (2,411)	$ (4,251)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	72	73
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 173	$ 433
Debt Securities in an unrealized loss position less than 12 months, unrealized losses		(1)
Debt Securities in an unrealized loss position 12 months or longer, fair value	60,832	62,467
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(1,777)	(2,548)
Debt Securities in an unrealized loss position, fair value	61,005	62,900
Debt Securities in an unrealized loss position, unrealized losses	$ (1,777)	$ (2,549)
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	112	116
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(10)	(6)
Debt Securities in an unrealized loss position, fair value	112	116
Debt Securities in an unrealized loss position, unrealized losses	$ (10)	$ (6)
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	5	4
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 120
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	3,982	3,947
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(41)	(80)
Debt Securities in an unrealized loss position, fair value	4,102	3,947
Debt Securities in an unrealized loss position, unrealized losses	$ (41)	$ (80)