Note 1 - Nature of Business and Significant Accounting Policies (Details Textual) - USD ($) $ / shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Equity Securities, FV-NI	$ 244,825
Allowance for Doubtful Accounts Receivable, Current, Ending Balance	0	0
Impairment of Long-Lived Assets Held-for-use	0	0
Accrued Royalty Income	93,594	84,333
Deposit Assets, Stumpage Agreements	$ 30,600	$ 94,600
Earnings Per Share, Diluted, Total	$ 0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total	$ 0
Taxes, Other	159,573	$ 154,167
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	58,893	$ 45,651
Mutual Fund [Member]
Equity Securities, FV-NI	$ 244,831