Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 27, 2015	Dec. 28, 2014
Current assets
Accounts receivable, allowance for doubtful accounts	$ 14,900	$ 15,900
Shareholders' equity
Preference stock, par value (in dollars per share)	$ 2.50	$ 2.50
Preference stock, shares authorized (in shares)	5,000,000	5,000,000
Preference stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.50	$ 0.50
Common stock, shares authorized (in shares)	600,000,000	600,000,000
Common stock, shares issued (in shares)	209,694,630	209,694,630
Treasury stock, at cost, shares (in shares)	84,899,200	85,168,478