Note 13 - Commitments and Contingencies (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments To Extend Notional Amount	$ 2,366,368,000	$ 2,062,241,000
Commitments to Fund Fixed Rate Loans	99,100,000
Commitments to Fund Adjustable Rate Loans	2,300,000,000
Operating Leases, Rent Expense	12,000,000	10,200,000	$ 9,300,000
Operating Leases, Income Statement, Sublease Revenue	$ 400,000	$ 400,000	$ 300,000
Minimum [Member]
Lessor, Operating Lease, Term of Contract	1 year
Maximum [Member]
Lessor, Operating Lease, Term of Contract	25 years