Note 8 - Loans (Details Textual) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016
Impaired Financing Receivable, Recorded Investment	$ 127,671,000		$ 127,671,000		$ 127,671,000	$ 115,074,000
Percentage Of Charge Off To Contractual Balances For Impaired Loans	7.10%		7.10%		7.10%	8.40%
Allowance for Credit Losses, Change in Method of Calculating Impairment	$ 678,000	$ 208,000	$ 678,000	$ 208,000	$ 678,000
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	305,000		305,000
Loans and Leases Receivable, Impaired, Commitment to Lend	0		0		0
Commercial Portfolio Segment [Member]
Allowance for Credit Losses, Change in Method of Calculating Impairment	636,000	208,000	636,000	208,000	636,000
Financing Receivable, Modifications, Subsequent Default, Recorded Investment			50,000
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down					2,100,000
Minimum [Member]
Period Loan Is In Payment Default			60 days
Maximum [Member]
Period Loan Is In Payment Default			90 days
Rate Reduction [Member] | Minimum [Member]
Troubled Debt Restructurings Length Of Modifications			90 days
Nonaccrual Loans [Member]
Impaired Financing Receivable, Recorded Investment	65,300,000		$ 65,300,000		65,300,000	$ 49,700,000
Accruing Troubled Debt Restructuring [Member]
Impaired Financing Receivable, Recorded Investment	62,400,000		62,400,000		62,400,000	65,400,000
Financing Receivable, Modifications, Recorded Investment	62,400,000		62,400,000		62,400,000	65,400,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	1,100,000		1,100,000		1,100,000	1,300,000
Non-accruing Troubled Debt Restructuring [Member]
Financing Receivable, Modifications, Recorded Investment	33,700,000		33,700,000		33,700,000	29,700,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	$ 143,000		$ 143,000		$ 143,000	$ 1,100,000