Note 6 - Fair Value Measurements - Reconciles Net Loss to Unrealized Loss on Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net gain recognized during the period on equity securities	$ 2,327	$ 1,278	$ 7,167	$ 125
Less: Net gain (loss) recognized during the period on equity securities sold during the period	0	(63)	237	(435)
Unrealized gain recognized during the reporting period on equity securities still held at the reporting date	$ 2,327	$ 1,341	$ 6,930	$ 560