Note 7 - Employee Benefit Plans (Details Textual) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	$ 2.2
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	0.6
Other Nonoperating Income (Expense) [Member]
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	$ 1.2	$ 0.7