Note 9 - Investments in Marketable Securities (Details Textual) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Equity Securities Fv Ni Gross Unrealized Gain	$ 116,851,000		$ 116,851,000		$ 110,081,000
Equity Securities Fv Ni Gross Unrealized Loss	20,000		20,000		34,000
Equity Securities, FV-NI, Unrealized Gain (Loss), Total	(54,000)	$ 12,448,000	6,784,000	$ (3,069,000)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2,907,000		2,907,000		335,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 187,000		187,000		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			30,103,000	4,399,000
Realized Investment Gains (Losses), Total			0	25,000
Proceeds from Sale and Maturity of Marketable Securities, Total			$ 0	$ 0