Note 5 - Loans Receivable and Allowance for Loan Losses - Impaired Loans (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Impaired loans, related allowance	$ 45,000		$ 45,000		$ 253,000
Impaired loans, recorded investment	9,400,000		9,400,000		6,800,000
Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	9,345,000		9,345,000		6,500,000
Impaired loans with no related allowance recorded, unpaid principal balance	10,086,000		10,086,000		7,295,000
Impaired loans with a related allowance recorded, recorded investment	45,000		45,000		253,000
Impaired loans with a related allowance recorded, unpaid principal balance	51,000		51,000		253,000
Impaired loans, related allowance	45,000		45,000		253,000
Impaired loans, recorded investment	9,390,000		9,390,000		6,753,000
Impaired loans, unpaid principal balance	10,137,000		10,137,000		7,548,000
Impaired loans with no related allowance recorded, average recorded investment	8,460,000	$ 8,673,000	7,828,000	$ 8,700,000
Impaired loans with no allowance recorded, interest income recognized	36,000	83,000	70,000	163,000
Impaired loans with a related allowance recorded, average recorded investment	296,000	232,000	246,000	232,000
Impaired loans with a related allowance recorded, interest income recognized
Impaired loans, average recorded investment	8,756,000	8,905,000	8,074,000	8,932,000
Impaired loans, interest income recognized	36,000	83,000	70,000	163,000
Commercial Real Estate Portfolio Segment [Member] | Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	4,071,000		4,071,000		1,977,000
Impaired loans with no related allowance recorded, unpaid principal balance	4,524,000		4,524,000		2,425,000
Impaired loans with a related allowance recorded, recorded investment
Impaired loans with a related allowance recorded, unpaid principal balance
Impaired loans, related allowance
Impaired loans, recorded investment	4,071,000		4,071,000		1,977,000
Impaired loans, unpaid principal balance	4,524,000		4,524,000		2,425,000
Impaired loans with no related allowance recorded, average recorded investment	3,250,000	6,188,000	2,770,000	6,213,000
Impaired loans with no allowance recorded, interest income recognized	25,000	75,000	49,000	148,000
Impaired loans with a related allowance recorded, average recorded investment
Impaired loans with a related allowance recorded, interest income recognized
Impaired loans, average recorded investment	3,250,000	6,188,000	2,770,000	6,213,000
Impaired loans, interest income recognized	25,000	75,000	49,000	148,000
Residential Portfolio Segment [Member] | Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	3,524,000		3,524,000		3,336,000
Impaired loans with no related allowance recorded, unpaid principal balance	3,557,000		3,557,000		3,369,000
Impaired loans with a related allowance recorded, recorded investment
Impaired loans with a related allowance recorded, unpaid principal balance
Impaired loans, related allowance
Impaired loans, recorded investment	3,524,000		3,524,000		3,336,000
Impaired loans, unpaid principal balance	3,557,000		3,557,000		3,369,000
Impaired loans with no related allowance recorded, average recorded investment	3,480,000	1,907,000	3,421,000	1,909,000
Impaired loans with no allowance recorded, interest income recognized	3,000	3,000	6,000	5,000
Impaired loans with a related allowance recorded, average recorded investment
Impaired loans with a related allowance recorded, interest income recognized
Impaired loans, average recorded investment	3,480,000	1,907,000	3,421,000	1,909,000
Impaired loans, interest income recognized	3,000	3,000	6,000	5,000
Commercial Portfolio Segment [Member] | Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	980,000		980,000		497,000
Impaired loans with no related allowance recorded, unpaid principal balance	1,163,000		1,163,000		683,000
Impaired loans with a related allowance recorded, recorded investment	45,000		45,000		251,000
Impaired loans with a related allowance recorded, unpaid principal balance	51,000		51,000		251,000
Impaired loans, related allowance	45,000		45,000		251,000
Impaired loans, recorded investment	1,025,000		1,025,000		748,000
Impaired loans, unpaid principal balance	1,214,000		1,214,000		934,000
Impaired loans with no related allowance recorded, average recorded investment	980,000	37,000	912,000	37,000
Impaired loans with no allowance recorded, interest income recognized
Impaired loans with a related allowance recorded, average recorded investment	293,000	232,000	244,000	232,000
Impaired loans with a related allowance recorded, interest income recognized
Impaired loans, average recorded investment	1,273,000	269,000	1,156,000	269,000
Impaired loans, interest income recognized
Consumer Portfolio Segment [Member] | Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	770,000		770,000		690,000
Impaired loans with no related allowance recorded, unpaid principal balance	842,000		842,000		818,000
Impaired loans with a related allowance recorded, recorded investment					2,000
Impaired loans with a related allowance recorded, unpaid principal balance					2,000
Impaired loans, related allowance					2,000
Impaired loans, recorded investment	770,000		770,000		692,000
Impaired loans, unpaid principal balance	842,000		842,000		$ 820,000
Impaired loans with no related allowance recorded, average recorded investment	750,000	541,000	725,000	541,000
Impaired loans with no allowance recorded, interest income recognized	8,000	5,000	15,000	10,000
Impaired loans with a related allowance recorded, average recorded investment	3,000		2,000
Impaired loans with a related allowance recorded, interest income recognized
Impaired loans, average recorded investment	753,000	541,000	727,000	541,000
Impaired loans, interest income recognized	$ 8,000	$ 5,000	$ 15,000	$ 10,000