Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Sep. 25, 2013	Dec. 26, 2012
Assets [Abstract]
Accumulated depreciation	$ 251,617	$ 250,173
Shareholders' equity
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	135,000	135,000
Common stock, shares issued	104,695	103,764
Common stock, shares outstanding	89,372	92,229
Treasury stock, at cost, shares	15,323	11,535