Note 5 - Loans - Troubled Debt Restructurings That Are Not Performing According to Their Restructured Terms (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts	0
Nonperforming Financial Instruments [Member]
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts	6	2
Recorded investment, not performing	$ 2,003	$ 1,785
Multi-family Residential Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts	1	1
Recorded investment, not performing	$ 383	$ 388
Taxi Medallion Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts	3
Recorded investment, not performing	$ 768
Commercial Business and Other Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts	2	1
Recorded investment, not performing	$ 852	$ 1,397