Note 3 - Investments (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale, Current, Total	$ 0	$ 33,758
Payments to Acquire Debt Securities, Available-for-sale	31,200	55,000
Proceeds from Sale and Maturity of Marketable Securities, Total	64,895	49,969	$ 18,649
Equity Securities, FV-NI	6,600	7,600
Equity Securities, FV-NI, Cost	7,700	5,700
Available-for-sale Equity Securities, Acquired During Period, Cost Basis	2,400	1,600
Equity Securities, FV-NI, Unrealized Gain (Loss), Total	$ (2,800)	(200)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax		$ 2,100