Note 6 - Retirement Plans (Details Textual) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020
Pension Plan [Member] | Gray Pension Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 3		$ 3
Profit Sharing Contribution [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	7		7
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 3		$ 6
Stock Issued During Period, Shares, Employee Benefit Plan (in shares)		430,899
Defined Contribution Plan, Employer Discretionary Contribution Amount, Common Stock		$ 4