Note 15 - Commitments and Contingencies (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Line Items]
Standby letters of credit	$ 14,326
Operating Leases, Rent Expense, Net	$ 645	$ 606	$ 621
Maximum [Member]
Commitments And Contingencies Disclosure [Line Items]
Standby letters of credit expiration period	1 year
Lessee Leasing Arrangements, Operating Leases, Renewal Term	10 years
Minimum [Member]
Commitments And Contingencies Disclosure [Line Items]
Lessee Leasing Arrangements, Operating Leases, Renewal Term	1 year