Note 7 - Securities Available for Sale - Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Less Than Twelve Months # of Investments	3	4
Less Than Twelve Months Fair Value	$ 10,291	$ 12,143
Less Than Twelve Months Unrealized Losses	$ (36)	$ (65)
Twelve Months or More # of Investments	1	5
Twelve Months or More Fair Value	$ 595	$ 20,637
Twelve Months or More Unrealized Losses	(105)	(56)
Total fair value	10,886	32,780
Total temporarily impaired securities	$ (141)	$ (121)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Less Than Twelve Months # of Investments	2	4
Less Than Twelve Months Fair Value	$ 10,254	$ 12,143
Less Than Twelve Months Unrealized Losses	$ (35)	$ (65)
Twelve Months or More # of Investments	0	0
Twelve Months or More Fair Value	$ 0	$ 0
Twelve Months or More Unrealized Losses	0	0
Total fair value	10,254
Total temporarily impaired securities		(65)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | US Government Agencies Debt Securities [Member]
Total fair value		$ 12,143
Other Marketable Securities [Member] | US Government Agencies Debt Securities [Member]
Less Than Twelve Months # of Investments		0
Less Than Twelve Months Fair Value		$ 0
Less Than Twelve Months Unrealized Losses		$ 0
Twelve Months or More # of Investments		4
Twelve Months or More Fair Value		$ 19,972
Twelve Months or More Unrealized Losses		(21)
Total fair value		19,972
Total temporarily impaired securities	$ (35)	$ (21)
Other Marketable Securities [Member] | Corporate Debt Securities [Member]
Less Than Twelve Months # of Investments	1
Less Than Twelve Months Fair Value	$ 37
Less Than Twelve Months Unrealized Losses	$ (1)
Twelve Months or More # of Investments	0
Twelve Months or More Fair Value	$ 0
Twelve Months or More Unrealized Losses	0
Total fair value	37
Total temporarily impaired securities	$ (1)
Other Marketable Securities [Member] | Preferred Stock [Member]
Less Than Twelve Months # of Investments	0	0
Less Than Twelve Months Fair Value	$ 0	$ 0
Less Than Twelve Months Unrealized Losses	$ 0	$ 0
Twelve Months or More # of Investments	1	1
Twelve Months or More Fair Value	$ 595	$ 665
Twelve Months or More Unrealized Losses	(105)	(35)
Total fair value	595	665
Total temporarily impaired securities	$ (105)	$ (35)