Note 9 - Securities Sold Under Agreements to Repurchase - Maturity of Short and Long-term Repurchase Agreements (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Short and long-term purchase agreements	$ 35,537	$ 36,370
US Government-sponsored Enterprises Debt Securities [Member]
Short and long-term purchase agreements	1,410	7,182
Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	34,127	29,188
Maturity Overnight [Member]
Short and long-term purchase agreements	33,627	33,682
Maturity Overnight [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Short and long-term purchase agreements	0	5,596
Maturity Overnight [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	33,627	28,086
Maturity Less than 30 Days [Member]
Short and long-term purchase agreements	200	1,203
Maturity Less than 30 Days [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Short and long-term purchase agreements	0	301
Maturity Less than 30 Days [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	200	902
Maturity 30 to 90 Days [Member]
Short and long-term purchase agreements	0	0
Maturity 30 to 90 Days [Member] | US Government-sponsored Enterprises Debt Securities [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	1,453	458
Maturity 90 Days to One Year [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Short and long-term purchase agreements	1,153	258
Maturity 90 Days to One Year [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	300	200
Maturity Over One Year to Four Years [Member]
Short and long-term purchase agreements	257	1,027
Maturity Over One Year to Four Years [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Short and long-term purchase agreements	257	1,027
Maturity Over One Year to Four Years [Member] | Residential Mortgage Backed Securities [Member]
Short and long-term purchase agreements	$ 0	$ 0