Note 15 - Stock-based Compensation - Fair Value of Each Option Using Black-scholes Valuation Model Assumptions (Details)					12 Months Ended			36 Months Ended
	Apr. 02, 2017	Nov. 03, 2015	Nov. 05, 2014	Feb. 11, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 02, 2017
Risk-free interest rates					1.90%	1.30%	1.40%
Expected life (in years) (Year)					3 years 36 days	4 years 182 days	4 years
Dividend yield					0.62%	1.10%	0.70%
Expected volatility					27.20%	30.70%	29.20%
Chief Executive Officer [Member] | Options to Purchase 300,000 Shares of Common Stock [Member]
Risk-free interest rates								2.36%
Expected life (in years) (Year)								7 years 91 days
Dividend yield								0.90%
Expected volatility								42.80%
Chief Executive Officer [Member] | Options to Purchase 100,000 Shares of Common Stock [Member]
Risk-free interest rates	1.64%
Expected life (in years) (Year)	4 years 273 days
Dividend yield	0.90%
Expected volatility	33.10%
2012 Incentive Plan [Member] | Chief Financial Officer [Member]
Risk-free interest rates		1.35%	1.30%	0.81%
Expected life (in years) (Year)		4 years	4 years	3 years 136 days
Dividend yield		0.70%	0.70%	0.80%
Expected volatility		29.20%	32.40%	33.50%
Forfeiture rate		0.00%	0.00%	0.00%