Note 3 - Securities - Available-for-sale Debt Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Less than 12 months, number of securities	3	11
Less than 12 months, fair value	$ 14,052	$ 12,187
Less than 12 months, gross unrealized losses	$ 87	$ 290
12 months or longer, number of securities	22	162
12 months or longer, fair value	$ 25,947	$ 231,017
12 months or longer, gross unrealized losses	$ 117	$ 5,745
Total, number of securities	25	173
Total, fair value	$ 39,999	$ 243,204
Total, gross unrealized losses	$ 204	$ 6,035
US States and Political Subdivisions Debt Securities [Member]
Less than 12 months, number of securities		3
Less than 12 months, fair value		$ 7,154
Less than 12 months, gross unrealized losses		$ 205
12 months or longer, number of securities	11	109
12 months or longer, fair value	$ 14,510	$ 112,563
12 months or longer, gross unrealized losses	$ 83	$ 2,090
Total, number of securities	11	112
Total, fair value	$ 14,510	$ 119,717
Total, gross unrealized losses	$ 83	$ 2,295
Residential Mortgage Backed Securities [Member]
Less than 12 months, number of securities	2
Less than 12 months, fair value	$ 13,059
Less than 12 months, gross unrealized losses	$ 80
12 months or longer, number of securities	3	14
12 months or longer, fair value	$ 7,034	$ 31,414
12 months or longer, gross unrealized losses	$ 28	$ 946
Total, number of securities	5	14
Total, fair value	$ 20,093	$ 31,414
Total, gross unrealized losses	$ 108	$ 946
Commercial Mortgage Backed Securities [Member]
Less than 12 months, number of securities
Less than 12 months, fair value
Less than 12 months, gross unrealized losses
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		25
Total, fair value		$ 73,640
Total, gross unrealized losses		$ 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	2	6
12 months or longer, fair value	$ 2,095	$ 10,294
12 months or longer, gross unrealized losses	$ 4	$ 278
Total, number of securities	2	7
Total, fair value	$ 2,095	$ 10,346
Total, gross unrealized losses	$ 4	$ 278
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Less than 12 months, number of securities		1
Less than 12 months, fair value		$ 950
Less than 12 months, gross unrealized losses		$ 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		1
Total, fair value		$ 950
Total, gross unrealized losses		$ 2
Corporate Debt Securities [Member]
Less than 12 months, number of securities	1	2
Less than 12 months, fair value	$ 993	$ 2,922
Less than 12 months, gross unrealized losses	$ 7	$ 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	1	2
Total, fair value	$ 993	$ 2,922
Total, gross unrealized losses	$ 7	$ 78
Asset-backed Securities [Member]
Less than 12 months, number of securities		1
Less than 12 months, fair value		$ 369
Less than 12 months, gross unrealized losses		$ 2
12 months or longer, number of securities	1	1
12 months or longer, fair value	$ 1,069	$ 1,433
12 months or longer, gross unrealized losses	$ 2	$ 21
Total, number of securities	1	2
Total, fair value	$ 1,069	$ 1,802
Total, gross unrealized losses	$ 2	$ 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	5	7
12 months or longer, fair value	$ 1,239	$ 1,673
12 months or longer, gross unrealized losses		$ 12
Total, number of securities	5	10
Total, fair value	$ 1,239	$ 2,413
Total, gross unrealized losses		$ 15