Note 4 - Investment Securities - Investment Securities With Unrealized Losses (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Less than 12 months fair value	$ 13,284,000	$ 45,748,000
Less than 12 months unrealized losses	60,000	553,000
12 months or more fair value	19,733,000	83,148,000
12 months or more unrealized losses	155,000	2,671,000
Total fair value	33,017,000	128,896,000
Total unrealized losses	215,000	3,224,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Less than 12 months fair value	10,319,000	26,478,000
Less than 12 months unrealized losses	31,000	269,000
12 months or more fair value	19,733,000	77,476,000
12 months or more unrealized losses	155,000	2,352,000
Total fair value	30,052,000	103,954,000
Total unrealized losses	186,000	2,621,000
US States and Political Subdivisions Debt Securities [Member]
Less than 12 months fair value	2,965,000	19,270,000
Less than 12 months unrealized losses	29,000	284,000
12 months or more fair value		5,672,000
12 months or more unrealized losses		319,000
Total fair value	2,965,000	24,942,000
Total unrealized losses	$ 29,000	$ 603,000