Note 6 - Retirement Plans (Details Textual) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Pension Plan [Member] | Gray Pension Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 3
Profit Sharing Contribution [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	13
Defined Contribution Plan, Employer Discretionary Contribution Amount	4
Defined Contribution Plan, Employer Discretionary Contribution Amount, Common Stock	$ 4