Note 5 - Qualified Affordable Housing Partnership Investments (Details Textual) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Proportional Amortization Method Qualified Affordable Housing Project Investments	$ 3,114		$ 3,114		$ 3,529
Proportional Amortization Method Qualified Affordable Housing Project Investments Unfunded Liability Obligation	329		$ 329		$ 361
Qualified Affordable Housing Project Investments Term			18 years
Proportional Amortization Method Qualified Affordable Housing Project Investments Amortization	$ 138	$ 177	$ 415	$ 512
Minimum [Member]
Qualified Affordable Housing Project Investments Return Rate			3.00%
Maximum [Member]
Qualified Affordable Housing Project Investments Return Rate			6.00%