Note 3 - Loans and Allowance for Loan Losses (Details Textual) - USD ($)		3 Months Ended			9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Loans and Leases Receivable, Net of Deferred Income, Total		$ 3,350,544,000			$ 3,350,544,000			$ 2,856,667,000
Loans and Leases Receivable Period Increase (Decrease)					$ 494,000,000
Loans and Leases Receivable, Percentage Period Increase (Decrease)					17.30%
Impaired Financing Receivable, Interest Income, Accrual Method, Total		200,000		$ 500,000	$ 800,000		$ 900,000
Loans and Leases Receivable, Nonaccrual Loans, Interest Income Recognized		0		0	0		0
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans		100,000		$ 100,000	$ 200,000		$ 100,000
Minimum Number of Days Past Due at Period End For Loans Modified as Troubled Debt Restructurings (Day)					30 days
Commercial Portfolio Segment [Member]
Loans and Leases Receivable, Net of Deferred Income, Total		2,938,361,000			$ 2,938,361,000			2,441,544,000
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Loans and Leases Receivable, Net of Deferred Income, Total	[1]	1,321,419,000			1,321,419,000			846,551,000
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | Grades 1-4 [Member]
Loans and Leases Receivable, Net of Deferred Income, Total		1,006,636,000	[2]		1,006,636,000	[2]		$ 521,920,000
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | SBA, CARES Act, Paycheck Protection Program [Member]
Loans and Leases Receivable, Net of Deferred Income, Total		555,000,000			555,000,000
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | SBA, CARES Act, Paycheck Protection Program [Member] | Grades 1-4 [Member]
Loans and Leases Receivable, Net of Deferred Income, Total		$ 555,000,000			$ 555,000,000

[1] For September 30, 2020, includes $555 million in loans originated under the Paycheck Protection Program.

[2] Included in Commercial and Industrial Loans Grades 1 – 4 are $555 million of loans originated under the Paycheck Protection Program.