Note 4 - Investments - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Available for sale securities, due in one year or less, amortized cost	$ 77,057
Available for sale securities, due in one year or less, fair value	77,248
Available for sale securities, due after one year through five years, amortized cost	27,326
Available for sale securities, due after one year through five years, fair value	27,708
Available for sale securities, due after five years through ten years, amortized cost	27,571
Available for sale securities, due after five years through ten years, fair value	28,152
Available for sale securities, due after ten years, amortized cost	2,500
Available for sale securities, due after ten years, fair value	2,626
Available for sale securities, mortgage backed securities, amortized cost	99,664
Available for sale securities, mortgage backed securities, fair value	103,925
Available for sale securities, amortized cost	234,118	$ 194,681
Available for sale securities, fair value	239,659	196,311
Held to maturity securities, due in one year or less, amortized cost	2,496
Held to maturity securities, due in one year or less, fair value	2,498
Held to maturity securities, due after one years through five years, amortized cost	19,033
Held to maturity securities, due after one year through five years, fair value	19,450
Held to maturity securities, due after five years through ten years, amortized cost	20,388
Held to maturity securities, due after five years through ten years, fair value	21,057
Held to maturity securities, due after ten years, amortized cost	6,801
Held to maturity securities, due after ten years, fair value	7,224
Held to maturity securities, amortized cost	48,718	52,231
Held to maturity securities, fair value	$ 50,229	$ 53,130