Note 14 - Benefit Plans (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employer Contribution under Medical and Dental Plan	$ 14,660	$ 14,992	$ 15,019
Payment for Pension Benefits	9,400	4,675
Defined Benefit Plan, Amortization of Gain (Loss)	$ (802)	(883)	(941)
Equity and Real Estate [Member] | Minimum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	75.00%
Equity and Real Estate [Member] | Maximum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	85.00%
Savings Plan 401(k) [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%
Defined Contribution Plan Percentage of Eligible Compensation	6.00%
Defined Contribution Plan, Cost	$ 4,193	$ 3,600	$ 3,400
Pension Plan [Member]
Defined Benefit Plan, Amortization of Gain (Loss)	802
Defined Benefit Plan, Expected Amortization, Next Fiscal Year, Total	$ 963
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.24%	3.60%
Other Pension Plan [Member]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.62%