Note 11 - Retirement Plans - Target Asset Allocation (Details)	Dec. 31, 2019
Large Cap Value [Member]
Target range	5.00%
Large Cap Value [Member] | Minimum [Member]
Target range	0.00%
Large Cap Value [Member] | Maximum [Member]
Target range	50.00%
Large Cap Blend [Member]
Target range	5.00%
Large Cap Blend [Member] | Minimum [Member]
Target range	0.00%
Large Cap Blend [Member] | Maximum [Member]
Target range	50.00%
Large Cap Growth [Member]
Target range	5.00%
Large Cap Growth [Member] | Minimum [Member]
Target range	0.00%
Large Cap Growth [Member] | Maximum [Member]
Target range	50.00%
Mid-cap Blend [Member]
Target range	15.00%
Mid-cap Blend [Member] | Minimum [Member]
Target range	0.00%
Mid-cap Blend [Member] | Maximum [Member]
Target range	40.00%
Small Cap Core [Member]
Target range	5.00%
Small Cap Core [Member] | Minimum [Member]
Target range	0.00%
Small Cap Core [Member] | Maximum [Member]
Target range	25.00%
Foreign Large Blend [Member]
Target range	10.00%
Foreign Large Blend [Member] | Minimum [Member]
Target range	0.00%
Foreign Large Blend [Member] | Maximum [Member]
Target range	40.00%
Emerging Markets [Member]
Target range	10.00%
Emerging Markets [Member] | Minimum [Member]
Target range	0.00%
Emerging Markets [Member] | Maximum [Member]
Target range	25.00%
Real Estate [Member]
Target range	5.00%
Real Estate [Member] | Minimum [Member]
Target range	0.00%
Real Estate [Member] | Maximum [Member]
Target range	20.00%
US Treasury Securities [Member]
Target range	5.00%
US Treasury Securities [Member] | Minimum [Member]
Target range	0.00%
US Treasury Securities [Member] | Maximum [Member]
Target range	25.00%
Intermediate Term Bond [Member]
Target range	10.00%
Intermediate Term Bond [Member] | Minimum [Member]
Target range	0.00%
Intermediate Term Bond [Member] | Maximum [Member]
Target range	50.00%
US Government Agencies Debt Securities [Member]
Target range	5.00%
US Government Agencies Debt Securities [Member] | Minimum [Member]
Target range	0.00%
US Government Agencies Debt Securities [Member] | Maximum [Member]
Target range	40.00%
High Yield Bond [Member]
Target range	10.00%
High Yield Bond [Member] | Minimum [Member]
Target range	0.00%
High Yield Bond [Member] | Maximum [Member]
Target range	25.00%
Emerging Markets Bond [Member]
Target range	10.00%
Emerging Markets Bond [Member] | Minimum [Member]
Target range	0.00%
Emerging Markets Bond [Member] | Maximum [Member]
Target range	20.00%
Money Market Funds [Member]
Target range	0.00%
Money Market Funds [Member] | Minimum [Member]
Target range	0.00%
Money Market Funds [Member] | Maximum [Member]
Target range	100.00%