Note 8 - Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	$ 281,723	$ 212,464
US Government Agencies Debt Securities [Member]
Securities available for sale	281,723	212,464
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	13,993	16,475
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale	13,993	16,475
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	1,144	1,319
Collateralized Mortgage Backed Securities [Member]
Securities available for sale	1,144	1,319
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	6,241	5,746
Corporate Debt Securities [Member]
Securities available for sale	6,241	5,746
Other Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	141	127
Other Securities [Member]
Securities available for sale	141	127
Fair Value, Inputs, Level 2 [Member]
Securities available for sale	303,242	236,131
Securities available for sale	$ 303,242	$ 236,131