Note 9 - Employee Benefit Plans (Details Textual) - USD ($)	1 Months Ended				2 Months Ended	12 Months Ended
	Nov. 30, 2018	Sep. 30, 2018	Jul. 31, 2018	Apr. 30, 2018	Feb. 20, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets						6.62%	6.80%
Defined Benefit Plan Assumed Long Term Rate Basis Spread						1.00%
Defined Benefit Plan, Plan Assets, Contributions by Employer						$ 10,565,000	$ 7,227,000
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 Contribution Plan, Employer Discretionary Contribution Amount						$ 4,000	114,000	$ 442,000
Capital Accumulation 401(K) Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer						$ 3,700,000	3,500,000	$ 3,500,000
Defined Contribution Plan, Employer Matching Contribution, Percent of Match						100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay						6.00%
Minimum [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent						2.00%
Minimum [Member] | Capital Accumulation 401(K) Plan [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent						1.00%
Maximum [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent						50.00%
Maximum [Member] | Capital Accumulation 401(K) Plan [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent						50.00%
Pension Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 2,100,000	$ 5,500,000	$ 1,200,000	$ 1,300,000
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year						$ 2,200,000
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year						600,000
Common Stock [Member]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount						9,300,000	$ 4,800,000
Nonoperating Income (Expense) [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Except Service cost						$ 2,800,000
Subsequent Event [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets					6.37%