Note 4 - Loans and Allowance for Credit Losses (Details Textual)		3 Months Ended
	Jan. 01, 2020 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2019	Apr. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Loans and Leases Receivable, Deferred Expense Income		$ 7,000,000			$ 7,000,000
Loans and Leases Receivable, Collateral for Secured Borrowings		1,700,000,000			1,600,000,000
Loans and Leases Receivable, Allowance, Initial Allowance on Acquired Loans		1,635,000
Allowance for Loan and Lease Losses, Period Increase (Decrease), Total		$ 15,400,000
Allowance for Loan and Lease Losses, Percentage Increase (Decrease) During the Period		57.00%
Loans and Leases Receivable, Net Amount, Total		$ 8,221,000
Financing Receivable, Modifications, Number of Contracts		0	0
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts			0
Mortgage Loans in Process of Foreclosure, Amount		$ 239,000			239,000
Loans and Leases Receivable, Net Amount, Total		2,895,223,000			2,818,225,000
Financial Asset Acquired with Credit Deterioration [Member]
Loans and Leases Receivable, Net Amount, Total					1,600,000
Subsequent Event [Member]
Financing Receivable, Number of Payment Deferrals				974
Financing Receivable, Deferred Payments				$ 413,000,000
Consumer Portfolio Segment [Member]
Loans and Leases Receivable, Allowance, Initial Allowance on Acquired Loans		34,000
Loans and Leases Receivable, Net Amount, Total		264,000
Financing Receivable, Overdraft Balance		538,000
Transfer of Loans From Purchased Credit Impaired to Purchased Credit Deteriorated [Member]
Loans and Leases Receivable, Allowance, Initial Allowance on Acquired Loans	$ 1,600,000
Loans and Leases Receivable, Net Amount, Total	$ 1,600,000
Directors and Executive Officers [Member]
Loans and Leases Receivable, Net Amount, Total		$ 41,000,000			$ 43,000,000