Note 15 - Employee Benefit Plans - Pension Plan's Weighted-Average Asset Allocations, by Asset Category (Details)	Dec. 31, 2019	Dec. 31, 2018
Defined benefit plan target asset allocations	100.00%	100.00%
Mutual Fund [Member] | Fixed Income Securities [Member]
Defined benefit plan target asset allocations	48.00%	52.00%
Mutual Fund [Member] | Equity Securities [Member]
Defined benefit plan target asset allocations	52.00%	48.00%
Defined Benefit Plan, Cash and Cash Equivalents [Member]
Defined benefit plan target asset allocations	0.00%	0.00%