Note 6 - Retirement Plans (Details Textual) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Defined Contribution Plan, Employer Discretionary Contribution Amount		$ 2,500
Capital Accumulation Plan [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 1,500	5,000
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	1,500	1,500
Gray Pension Plan [Member] | Pension Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	$ 0	$ 0