Note 2 - Stock-based Compensation - Valuation Assumptions (Details) - 2004 Employee Stock Plan [Member] - Employee Stock Purchase Plan [Member]	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Expected term (years) (Year)	182 days	182 days	182 days	182 days
Expected volatility	23.50%	27.50%	23.50%	28.60%
Risk-free interest rate	1.20%	0.50%	0.90%	0.40%
Dividend yield	0.80%	1.10%	0.90%	1.20%