Note 9 - Marketable Securities (Details Textual) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions		1 Months Ended		12 Months Ended
	Jun. 25, 2020	Oct. 31, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Marketable Securities, Gain (Loss), Total				$ 594,753	$ 829	$ (3,487)
Proceeds from Sale of Cost Method Investments				227,270	0	0
Realized Investment Gains (Losses), Total				190,832	0	$ 0
Marketable Securities, Total				$ 706,954	$ 9,353
Common Stock, Dividends, Per Share, Declared (in dollars per share)				$ 0.54000	$ 1.12000	$ 1.12000
Albertsons Companies, Inc [Member]
Proceeds from Issuance of Convertible Preferred Stock			$ 1,680,000
Percentage of Ownership to Be Purchased			17.50%
Common Stock, Dividends, Per Share, Declared (in dollars per share)		$ 0.10
Albertsons Companies, Inc [Member] | IPO [Member]
Stock Issued During Period, Shares, New Issues (in shares)	50.0
Sale of Stock, Price Per Share (in dollars per share)	$ 16.00
Albertsons Companies, Inc [Member] | Convertible Preferred Stock [Member]
Stock Issued During Period, Value, New Issues			$ 1,750,000
Albertsons Companies, Inc [Member]
Percentage of Ownership in Cost Method Investment			7.50%	9.29%
Proceeds from Sale of Cost Method Investments	$ 71,400		$ 156,100
Realized Investment Gains (Losses), Total	$ 59,200		$ 131,600
Shares Sold in Cost Method Investments (in shares)	4.7
Investment Owned, Balance, Shares (in shares)				39.8
Marketable Securities, Total				$ 700,400
Marketable Securities, Unrealized Gain (Loss), Total				596,800
Proceeds from Dividends Received				4,000
Albertsons Companies, Inc [Member] | Other Assets [Member]
Other Investments and Securities, at Cost				$ 140,200