Note 8 - Investments in Marketable Securities (Details Textual) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Securities Fv Ni Gross Unrealized Gain	$ 110,081,000				$ 110,081,000	$ 108,934,000
Equity Securities Fv Ni Gross Unrealized Loss	34,000				34,000	24,000
Equity Securities, FV-NI, Unrealized Gain (Loss), Total	721,000	$ 3,486,000	$ 12,448,000	$ (15,517,000)	1,138,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	335,000				335,000	823,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 3,809,000				3,809,000	1,705,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Total					0	0
Proceeds from Sale of Debt Securities, Available-for-sale					4,539,000	50,197,000	34,642,000
Realized Investment Gains (Losses), Total					18,000	262,000	816,000
Proceeds from Sale and Maturity of Marketable Securities, Total					$ 0	$ 0	$ 0