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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Expected term (years)	182 days	182 days	182 days	182 days
Expected volatility	27.50%	24.80%	28.60%	30.30%
Risk-free interest rate	0.50%	0.20%	0.40%	0.20%
Dividend yield	1.10%	1.60%	1.20%	1.40%