Note 8 - Employee Benefit Plans (Details Textual) - USD ($)	1 Months Ended		12 Months Ended
	Feb. 10, 2020	May 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets			6.37%	6.62%
Defined Benefit Plan Assumed Long Term Rate Basis Spread			1.00%
Defined Benefit Plan, Plan Assets, Contributions by Employer			$ 4,095,000	$ 10,565,000
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			$ 10,000	4,000	$ 114,000
Capital Accumulation 401(K) Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer			$ 3,900,000	3,700,000	$ 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		$ 3,600,000
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year			$ 6,800,000
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			14,700,000	9,300,000
Nonoperating Income (Expense) [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Except Service cost			$ 5,000,000.0	$ 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	6.45%