Note 3 - Available-for-sale Securities - Investment Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale securities in continuous loss position, less than 12 months, fair value	$ 2,457	$ 8,024
Available-for-sale securities in continuous loss position, less than 12 months, unrealized loss	(17)	(38)
Available-for-sale securities in continuous loss position, 12 months or more, fair value	16,633	18,396
Available-for-sale securities in continuous loss position, 12 months or more, unrealized loss	(1,083)	(1,184)
Available-for-sale securities in continuous loss position, fair value	19,090	26,420
Available-for-sale securities in continuous loss position, unrealized loss	(1,100)	(1,222)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available-for-sale securities in continuous loss position, less than 12 months, fair value	2,457	8,024
Available-for-sale securities in continuous loss position, less than 12 months, unrealized loss	(17)	(38)
Available-for-sale securities in continuous loss position, 12 months or more, fair value	3,661	5,422
Available-for-sale securities in continuous loss position, 12 months or more, unrealized loss	(55)	(158)
Available-for-sale securities in continuous loss position, fair value	6,118	13,446
Available-for-sale securities in continuous loss position, unrealized loss	(72)	(196)
Corporate Debt Securities [Member]
Available-for-sale securities in continuous loss position, less than 12 months, fair value
Available-for-sale securities in continuous loss position, less than 12 months, unrealized loss
Available-for-sale securities in continuous loss position, 12 months or more, fair value	12,972	12,974
Available-for-sale securities in continuous loss position, 12 months or more, unrealized loss	(1,028)	(1,026)
Available-for-sale securities in continuous loss position, fair value	12,972	12,974
Available-for-sale securities in continuous loss position, unrealized loss	$ (1,028)	$ (1,026)