Condensed Consolidated Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jun. 29, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accumulated depreciation	$ 264,224	$ 252,611
Preferred stock, par value (in usd per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	200,000	200,000
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, shares issued (in shares)	29,498,470	29,141,467
Common stock held in treasury, at cost (in shares)	1,492,623	1,325,975