Note 6 - Loans and the Allowance for Loan Losses - (Details Textual) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans and Leases Receivable, Deferred Income		$ 1,300,000	$ 761,000
Loans and Leases Receivable Reclassified from Overdraft		129,000	232,000
Loans Receivable, Unpaid Principal Balance		82,400,000	55,500,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	[1]	696,000	1,776,000
Loans and Leases Receivable, Net of Deferred Income		975,284,000	810,951,000
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing		132,000	168,000
Financing Receivable, Recorded Investment, Nonaccrual Status		12,535,000	7,126,000
Impaired Financing Receivable, Interest Income, Accrual Method		247,000	464,000
Financing Receivable, Modifications, Subsequent Default, Recorded Investment		3,300,000	0
American Gateway Financial Corporation [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net		696,000	1,776,000	$ 3,634,000
American Gateway Financial Corporation [Member] | Performing Financial Instruments [Member]
Loans and Leases Receivable, Deferred Income		1,800,000	2,400,000
Loans Receivable, Fair Value Disclosure		46,100,000	65,300,000
Loans and Leases Receivable, Net of Deferred Income		$ 47,200,000	$ 65,900,000

[1] Purchased credit impaired loans are evaluated for impairment on an individual basis.