Note 8 - Retirement Plans (Details Textual) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Stock Issued During Period, Value, Employee Benefit Plan	$ 4,000
Common Stock [Member]
Stock Issued During Period, Value, Employee Benefit Plan	4,000
Capital Accumulation Plan [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	3,000
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	13,000
Capital Accumulation Plan [Member] | Common Stock [Member]
Stock Issued During Period, Value, Employee Benefit Plan	4,000
Pension Plan [Member] | Gray Pension Plan [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	0
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 2,000