Note 7 - Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2015	Sep. 27, 2014	Sep. 26, 2015	Sep. 27, 2014
Net income	$ 11,324	$ 29,940	$ 60,003	$ 79,907
Basic (in shares)	22,581	22,536	22,623	22,536
Net effect of dilutive stock options and restricted share units (in shares)	112	153	148	186
Average shares - Diluted (in shares)	22,693	22,689	22,771	22,722
Net income per share (see Note 7):
Basic (in dollars per share)	$ 0.50	$ 1.33	$ 2.65	$ 3.55
Diluted (in dollars per share)	$ 0.50	$ 1.32	$ 2.64	$ 3.52