Note 14 - Retirement Plans - Plan's Asset Allocations by Asset Category (Details)		Dec. 31, 2019	Dec. 31, 2018
Equity Securities [Member]
Asset category, plan asset allocations	[1]	66.00%	64.00%
Debt Securities [Member]
Asset category, plan asset allocations	[1]	33.00%	35.00%
Other/Cash [Member]
Asset category, plan asset allocations		1.00%	1.00%
Minimum [Member] | Equity Securities [Member]
Asset category		50.00%
Minimum [Member] | Fixed Income Securities [Member]
Asset category		20.00%
Minimum [Member] | Cash Equivalents [Member]
Asset category		0.00%
Maximum [Member] | Equity Securities [Member]
Asset category		80.00%
Maximum [Member] | Fixed Income Securities [Member]
Asset category		50.00%
Maximum [Member] | Cash Equivalents [Member]
Asset category		5.00%

[1] May include mutual funds comprised of both stocks and bonds.