Note 8 - Employee Benefit Plans (Details) - USD ($)		1 Months Ended	12 Months Ended
		Jan. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase					2.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets				7.20%	7.20%
Long-term Investments (in Dollars)				$ 1,515,000	$ 4,920,000
Defined Benefit Plan Assumed Long Term Rate Basis Spread				1.00%
Defined Benefit Plan, Fair Value of Plan Assets (in Dollars)				$ 73,321,000	74,551,000	$ 69,051,000
Defined Benefit Plan, Contributions by Employer (in Dollars)		$ 4,900,000		$ 5,460,000	6,715,000
Defined Contribution Plan, Employer Matching Contribution, Percent of Match				55.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay				5.00%
Defined Benefit Plan Months of Services Required for Eligibility				6 months
Defined Contribution Plan, Employer Discretionary Contribution Amount (in Dollars)				$ 391,000	292,000	293,000
Years 1 Through 5 [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Cash Balance Pay Credit Percentage				3.00%
Years 6 Through 10 [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Cash Balance Pay Credit Percentage				4.50%
After 10 Years [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Cash Balance Pay Credit Percentage				6.00%
Assumed for 2016 Through 2018 [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	[1]			0.00%
Assumed for after 2018 [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	[1]			2.00%
Scenario, Forecast [Member] | Unfunded Supplemental Executive Retirement Plan [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year (in Dollars)			$ 400,000
Common Stock [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Long-term Investments (in Dollars)				$ 4,300,000	$ 1,400,000
Defined Benefit Plan, Actual Plan Asset Allocations				6.00%	2.00%
Pension Compensation [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent				6.00%
Pension Compensation in Excess of Social Security Wages [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent				5.70%
Capital Accumulation 401(k) Plan [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Contributions by Employer (in Dollars)				$ 3,400,000	$ 3,200,000	$ 3,000,000
Defined Contribution Plan, Employer Matching Contribution, Percent of Match				100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay				6.00%
Common Stock [Member] | Scenario, Forecast [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year (in Dollars)			$ 5,300,000
Minimum [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent				2.00%
Minimum [Member] | Capital Accumulation 401(k) Plan [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent				1.00%
Maximum [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent				50.00%
Maximum [Member] | Capital Accumulation 401(k) Plan [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent				50.00%
Fair Value, Inputs, Level 3 [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets (in Dollars)				$ 19,000,000	22,100,000
Fair Value, Inputs, Level 3 [Member] | Real Estate [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets (in Dollars)				13,200,000	11,300,000
Fair Value, Inputs, Level 3 [Member] | Collective Investment Funds [Member]
Note 8 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets (in Dollars)				$ 5,800,000
Deferred Compensation Plan Assets (in Dollars)					$ 10,800,000

[1] 0% is assumed for years 2016 through 2018 and 2% is assumed thereafter.