Note 6 - Summary of Unrealized and Realized Gains and Losses Recognized in Net Income on Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Net gains recognized during the period on equity securities	$ 665	$ 912	$ 1,865	$ 837
Less: Net gains recognized during the period on equity securities sold during the period	970	181	1,599	311
Net unrealized (losses) gains recognized during the reporting period on equity securities still held at the reporting date	$ (305)	$ 731	$ 266	$ 526