Note 6 - Investments in Affordable Housing and Alternative Energy Partnerships - Investments in Affordable Housing and Alternative Energy Partnerships (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments in affordable housing partnerships, net	$ 260,112	$ 236,787
Other borrowings for affordable housing limited partnerships	17,481	17,661
Investments in affordable housing pertnerships, unfunded commitments	124,657	115,038
Investments in alternative energy tax credit partnerships, net	$ 12,759	$ 14,290