Note 4 - Investments - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available for sale securities, due in one year or less, amortized cost	$ 20,744
Available for sale securities, due in one year or less, fair value	20,921
Available for sale securities, due after one year through five years, amortized cost	1,559
Available for sale securities, due after one year through five years, fair value	1,571
Available for sale securities, due after five years through ten years, amortized cost	29,604
Available for sale securities, due after five years through ten years, fair value	30,792
Available for sale securities, due after ten years, amortized cost	47,003
Available for sale securities, due after ten years, fair value	47,590
Available for sale securities, mortgage backed securities, amortized cost	79,739
Available for sale securities, mortgage backed securities, fair value	83,344
Available for sale securities, amortized cost	178,649	$ 194,681
Available for sale securities, fair value	184,218	196,311
Held to maturity securities, due in one year or less, amortized cost	2,304
Held to maturity securities, due in one year or less, fair value	2,315
Held to maturity securities, due after one years through five years, amortized cost	18,275
Held to maturity securities, due after one year through five years, fair value	18,923
Held to maturity securities, due after five years through ten years, amortized cost	21,999
Held to maturity securities, due after five years through ten years, fair value	23,267
Held to maturity securities, due after ten years, amortized cost	20,628
Held to maturity securities, due after ten years, fair value	21,469
Held to maturity securities, amortized cost	63,206	52,231
Held to maturity securities, fair value	$ 65,974	$ 53,130