Note 6 - Retirement Plans (Details Textual) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)
Defined Benefit Plan, Plan Assets, Contributions by Employer		$ 0.6
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 1.7	1.7
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 1.8	3.7
Defined Contribution Plan, Expected Contributions In Next Twelve Months		$ 3.2