Note 4 - Securities - Available-for-sale Debt Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Less than 12 months, number of securities	21	11
Less than 12 months, fair value	$ 61,748	$ 12,187
Less than 12 months, gross unrealized losses	$ 506	$ 290
12 months or longer, number of securities		162
12 months or longer, fair value		$ 231,017
12 months or longer, gross unrealized losses		$ 5,745
Total, number of securities	21	173
Total, fair value	$ 61,748	$ 243,204
Total, gross unrealized losses	$ 506	$ 6,035
US States and Political Subdivisions Debt Securities [Member]
Less than 12 months, number of securities	10	3
Less than 12 months, fair value	$ 19,436	$ 7,154
Less than 12 months, gross unrealized losses	$ 359	$ 205
12 months or longer, number of securities		109
12 months or longer, fair value		$ 112,563
12 months or longer, gross unrealized losses		$ 2,090
Total, number of securities	10	112
Total, fair value	$ 19,436	$ 119,717
Total, gross unrealized losses	$ 359	$ 2,295
Residential Mortgage Backed Securities [Member]
Less than 12 months, number of securities	4
Less than 12 months, fair value	$ 19,934
Less than 12 months, gross unrealized losses	$ 92
12 months or longer, number of securities		14
12 months or longer, fair value		$ 31,414
12 months or longer, gross unrealized losses		$ 946
Total, number of securities	4	14
Total, fair value	$ 19,934	$ 31,414
Total, gross unrealized losses	$ 92	$ 946
Commercial Mortgage Backed Securities [Member]
Less than 12 months, number of securities	1
Less than 12 months, fair value	$ 2,500
Less than 12 months, gross unrealized losses	$ 11
12 months or longer, number of securities		25
12 months or longer, fair value		$ 73,640
12 months or longer, gross unrealized losses		$ 2,398
Total, number of securities	1	25
Total, fair value	$ 2,500	$ 73,640
Total, gross unrealized losses	$ 11	$ 2,398
Collateralized Mortgage Backed Securities [Member]
Less than 12 months, number of securities		1
Less than 12 months, fair value		$ 52
Less than 12 months, gross unrealized losses
12 months or longer, number of securities		6
12 months or longer, fair value		$ 10,294
12 months or longer, gross unrealized losses		$ 278
Total, number of securities		7
Total, fair value		$ 10,346
Total, gross unrealized losses		$ 278
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Less than 12 months, number of securities	4	1
Less than 12 months, fair value	$ 18,990	$ 950
Less than 12 months, gross unrealized losses	$ 43	$ 2
12 months or longer, number of securities
12 months or longer, fair value
12 months or longer, gross unrealized losses
Total, number of securities	4	1
Total, fair value	$ 18,990	$ 950
Total, gross unrealized losses	$ 43	$ 2
Corporate Debt Securities [Member]
Less than 12 months, number of securities		2
Less than 12 months, fair value		$ 2,922
Less than 12 months, gross unrealized losses		$ 78
12 months or longer, number of securities		0
12 months or longer, fair value		$ 0
12 months or longer, gross unrealized losses		$ 0
Total, number of securities		2
Total, fair value		$ 2,922
Total, gross unrealized losses		$ 78
Asset-backed Securities [Member]
Less than 12 months, number of securities	2	1
Less than 12 months, fair value	$ 888	$ 369
Less than 12 months, gross unrealized losses	$ 1	$ 2
12 months or longer, number of securities		1
12 months or longer, fair value		$ 1,433
12 months or longer, gross unrealized losses		$ 21
Total, number of securities	2	2
Total, fair value	$ 888	$ 1,802
Total, gross unrealized losses	$ 1	$ 23
Negotiable Certificates of Deposit [Member]
Less than 12 months, number of securities		3
Less than 12 months, fair value		$ 740
Less than 12 months, gross unrealized losses		$ 3
12 months or longer, number of securities		7
12 months or longer, fair value		$ 1,673
12 months or longer, gross unrealized losses		$ 12
Total, number of securities		10
Total, fair value		$ 2,413
Total, gross unrealized losses		$ 15