Note 4 - Earnings Per Share - Calculation of Income (Loss) Per Shares (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2017	Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2017
Net Income	$ 8,172	$ 8,172	$ 19,439	$ 19,439	$ 43,858	$ 48,924	$ 48,924
Shares for Basic Earnings Per Share (in shares)	59,496		61,018		59,553	62,630
Dilutive Effect of Stock Options (in shares)	40		42		41	42
Shares for Diluted Earnings Per Share (in shares)	59,536		61,060		59,594	62,672
Participating Securities [Member]
Net Income	$ 100		$ 100		$ 400	$ 400
Weighted Average Shares Outstanding (in shares)	58,917		60,555		58,974	62,167
Participating Securities (in shares)	579		463		579	463