Note 8 - Investments in Marketable Securities (Details Textual) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity Securities Fv Ni Gross Unrealized Gain	$ 122,290,000				$ 110,081,000				$ 122,290,000	$ 110,081,000
Equity Securities Fv Ni Gross Unrealized Loss	13,000				34,000				13,000	34,000
Equity Securities, FV-NI, Unrealized Gain (Loss), Total	(3,866,000)	$ 9,312,000	$ (54,000)	$ 6,838,000	721,000	$ 3,486,000	$ 12,448,000	$ (15,517,000)	12,230,000	1,138,000	$ 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	3,407,000				335,000				3,407,000	335,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 167,000				$ 3,809,000				167,000	3,809,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Total									0	0
Proceeds from Sale of Debt Securities, Available-for-sale									44,500,000	4,539,000	50,197,000
Realized Investment Gains (Losses), Total									127,000	18,000	262,000
Proceeds from Sale and Maturity of Marketable Securities, Total									$ 0	$ 0	$ 0