Note 8 - Benefit Plans (Details Textual)	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Defined Benefit Plans Number of Plans	2
Defined Benefit Plans Retirement Age	65 years
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Funded Status	$ 9,467,000	$ 8,925,000
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year	1,108,000
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	1,500,000
Defined Benefit Plan, Funded Status of Plan	(9,467,000)	(8,925,000)
Deferred Compensation Liability, Classified, Noncurrent	$ 962,000
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	25.00%
Defined Contribution Plan, Employer Discretionary Contribution, Percent	3.00%
Pension Contributions	$ 1,069,000	$ 903,000	$ 782,000
Postretirement Life Insurance [Member]
Cash Surrender Value of Life Insurance	972,000
Postretirement Life Insurance [Member] | Life Insurance Contracts [Member]
Gain (Loss) on Investments	78,000
Non-Qualified Deferred Compenstion Plan [Member]
Defined Benefit Plan, Funded Status of Plan	$ 960,000