Note 6 - Marketable Securities (Details Textual) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions		3 Months Ended		6 Months Ended
	Jun. 25, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Marketable Securities, Gain (Loss), Total		$ 526,243	$ 71	$ 521,577	$ 1,574
Proceeds from Sale of Cost Method Investments				227,521	0
Realized Investment Gains (Losses), Total		190,832	$ 0	190,832	$ 0
Marketable Securities, Total		$ 633,551		633,551		$ 9,353
Albertsons Companies, Inc [Member]
Proceeds from Issuance of Convertible Preferred Stock				$ 1,680,000
Percentage of Ownership to Be Purchased		17.50%		17.50%
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%		7.50%		9.29%
Proceeds from Sale of Cost Method Investments	$ 71,400			$ 156,100
Realized Investment Gains (Losses), Total				$ 131,600
Shares Sold in Cost Method Investments (in shares)	4.7
Investment Owned, Balance, Shares (in shares)		39.8		39.8
Marketable Securities, Total		$ 628,200		$ 628,200
Marketable Securities, Unrealized Gain (Loss), Total				$ 524,700
Albertsons Companies, Inc [Member] | Gain on Sale of Cost Method Investment [Member]
Realized Investment Gains (Losses), Total	$ 59,200
Albertsons Companies, Inc [Member] | Other Assets [Member]
Other Investments and Securities, at Cost						$ 140,200