Note 10 - Financial Instrument Commitments (Details Textual)	6 Months Ended
	Jun. 30, 2018 USD ($)
Commitments And Contingencies Disclosure [Line Items]
Standby letters of credit	$ 17,708,000
Maximum [Member]
Commitments And Contingencies Disclosure [Line Items]
Standby letters of credit expiration period	1 year