Note 6 - Employee Stock Benefit Plans - Weighted-average Assumptions to Value Share-based Awards Granted (Details) - $ / shares	12 Months Ended
	Dec. 30, 2017		Dec. 31, 2016		Dec. 26, 2015
Employee Stock Option [Member]
Dividend yield		[1]		[1]	2.10%
Expected volatility		[1]		[1]	39.10%
Risk-free interest rate		[1]		[1]	1.60%
Expected term (years) (Year)		[1]		[1]	5 years 328 days
Weighted-average grant date fair value per share (in dollars per share)		[1]		[1]	$ 3.46
Restricted Stock Units (RSUs) [Member]
Dividend yield	1.40%		2.00%		2.10%
Employee Stock Purchase Plan [Member]
Dividend yield	1.40%		2.00%		2.20%
Expected volatility	33.30%		31.20%		35.30%
Risk-free interest rate	0.70%		0.30%		0.10%
Expected term (years) (Year)	182 days		182 days		182 days
Weighted-average grant date fair value per share (in dollars per share)	$ 4.63		$ 2.82		$ 2.71

[1] There were no employee stock options granted in 2017 and 2016.