Note 11 - Investments in Marketable Securities (Details Textual) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Equity Securities Fv Ni Gross Unrealized Gain	$ 76,151,000		$ 76,151,000		$ 98,445,000
Equity Securities Fv Ni Gross Unrealized Loss	1,067,000		1,067,000		134,000
Equity Securities, FV-NI, Unrealized Gain (Loss), Total	(23,797,000)	$ (241,000)	(23,227,000)	$ (40,580,000)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	4,288,000		4,288,000		6,759,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	796,000		796,000		$ 361,000
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0	$ 0	0	0
Proceeds from Sale and Maturity of Marketable Securities, Total			89,129,000	28,004,000
Debt Securities, Realized Gain (Loss), Total			$ 941,000	$ 135,000