Note 1 - Significant Accounting Policies and Recent Accounting Pronouncements (Details Textual) - USD ($) $ / shares in Thousands		12 Months Ended
	Apr. 12, 2018	Dec. 31, 2019	Dec. 31, 2018
Equity Securities, FV-NI		$ 500,642	$ 244,825
Accounts Receivable, Allowance for Credit Loss, Current		0
Impairment of Long-Lived Assets Held-for-use		0	0
Accrued Royalty Income		84,880	93,594
Deposit Assets, Stumpage Agreements		$ 87,300	$ 54,300
Earnings Per Share, Diluted, Total		$ 0	$ 0
Payments of Ordinary Dividends, Common Stock	$ 233,099	$ 0	$ 233,099
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total		0
Taxes, Other		151,204	159,573
Oil and Gas [Member]
Capitalized Contract Cost, Net, Total		0
Timber [Member]
Contract with Customer, Liability, Total		10,407	9,466
Surface Leases [Member]
Contract with Customer, Liability, Total		7,499	15,403
Surface Leases [Member] | Accounts Payable and Accrued Liabilities [Member]
Contract with Customer, Liability, Total		77,857	58,893
Mutual Fund [Member]
Equity Securities, FV-NI		$ 500,642	$ 244,825