Note 8 - Benefit Plans (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plans Number of Plans	2
Defined Benefit Plans Retirement Age	65 years
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ (6,241)	$ (9,467)
Other Assets [Member] | Nonqualified Plan [Member]
Cash Surrender Value of Life Insurance	2,200
Other Noncurrent Liabilities [Member] | Nonqualified Plan [Member]
Deferred Compensation Liability, Classified, Noncurrent	2,200
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(8,400)
Pension Plan [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	2,200
Defined Benefit Plan, Expected Amortization, Next Fiscal Year	(1,100)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	100
Postretirement Life Insurance [Member]
Cash Surrender Value of Life Insurance	2,200
Postretirement Life Insurance [Member] | Life Insurance Contracts [Member]
Gain (Loss) on Investments	300
401(K) Plan [Member}
Defined Contribution Plan, Employer Matching Contribution, Percent of Match		25.00%
Defined Contribution Plan, Employer Discretionary Contribution, Percent		3.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 1,000	$ 1,100	$ 900