Note 14 - Commitments and Off-balance-sheet Risk - Instruments Carried at Fair Values (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Standby letters of credit, carrying value	$ 1,012,197,000	$ 821,338,000
Standby Letters of Credit [Member]
Standby letters of credit, contract amount	26,030,000	26,202,000
Standby letters of credit, carrying value	$ 122,000	$ 156,000