Note 1 - Significant Accounting Policies and Recent Accounting Pronouncements (Details Textual) - USD ($) $ / shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Equity Securities, FV-NI	$ 246,528		$ 244,825
Accounts Receivable, Allowance for Credit Loss, Current	0	$ 0
Impairment of Long-Lived Assets Held-for-use	0	$ 0
Accrued Royalty Income	58,626		93,594
Deposit Assets, Stumpage Agreements	$ 54,300		54,300
Earnings Per Share, Diluted, Total	$ 0	$ 0
Oil and Gas [Member]
Capitalized Contract Cost, Net, Total	$ 0
Timber [Member]
Capitalized Contract Cost, Net, Total	0
Surface Leases [Member] | Accounts Payable and Accrued Liabilities [Member]
Contract with Customer, Liability, Total	70,780		58,893
Mutual Fund [Member]
Equity Securities, FV-NI	$ 246,528		$ 244,825