Note 11 - Long-term Debt - Summary of Long-term Debt (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Long-term debt	$ 100	$ 100
Less current portion
Long-term debt, noncurrent	$ 100	100
Line of Credit [Member]
Long-term debt, weighted average interest rate	3.20%
Long-term debt, maturities	2020
Long-term debt	$ 90	90
Unsecured Term Note Payable [Member]
Long-term debt, weighted average interest rate	4.00%
Long-term debt, maturities	2028
Long-term debt	$ 10	$ 10