Note 13 - Commitments and Contingencies (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments To Extend Notional Amount	$ 2,691,579,000	$ 2,366,368,000
Commitments to Fund Fixed Rate Loans	200,400,000
Commitments to Fund Adjustable Rate Loans	2,500,000,000
Operating Leases, Rent Expense, Total	12,100,000	12,000,000	$ 10,200,000
Operating Leases, Income Statement, Sublease Revenue	$ 400,000	$ 400,000	$ 400,000
Minimum [Member]
Lessor, Operating Lease, Term of Contract	1 year
Maximum [Member]
Lessor, Operating Lease, Term of Contract	10 years 182 days