Note 8 - Retirement Plans - Allocation of Plan Assets (Details)	Dec. 31, 2016	Dec. 31, 2015
Asset category:
Plan assets, percent	100.00%	100.00%
Insurance General Account [Member]
Asset category:
Plan assets, percent	23.00%	26.00%
Cash and Cash Equivalents [Member]
Asset category:
Plan assets, percent	6.00%	2.00%
Equity Securities [Member]
Asset category:
Plan assets, percent	39.00%	54.00%
Fixed Income Securities [Member]
Asset category:
Plan assets, percent	28.00%	14.00%
Real Estate [Member]
Asset category:
Plan assets, percent	4.00%	4.00%