Note 6 - Fair Value Measurements - Reconciles Net Loss to Unrealized Loss 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
Net gain recognized during the period on equity securities	$ 767	$ 3,004	$ 7,934	$ 3,129
Less: Net gain (loss) recognized during the period on equity securities sold during the period	299	(21)	536	(484)
Unrealized gain recognized during the reporting period on equity securities still held at the reporting date	$ 468	$ 3,025	$ 7,398	$ 3,613