Note 10 - Securities Sold Under Agreements to Repurchase - Maturity of Short and Long-term Repurchase Agreements (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Short and long-term purchase agreements	$ 33,343	$ 34,252
Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	33,343	34,252
Maturity Overnight [Member]
Short and long-term purchase agreements	31,431	32,341
Maturity Overnight [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	31,431	32,341
Maturity Less than 30 Days [Member]
Short and long-term purchase agreements	254	1,200
Maturity Less than 30 Days [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	254	1,200
Maturity 30 to 90 Days [Member]
Short and long-term purchase agreements	0	0
Maturity 30 to 90 Days [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	0	0
Maturity 90 Days to One Year [Member]
Short and long-term purchase agreements	1,400	454
Maturity 90 Days to One Year [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	1,400	454
Maturity Over One Year to Four Years [Member]
Short and long-term purchase agreements	258	257
Maturity Over One Year to Four Years [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	$ 258	$ 257