Shareholders' equity Summary of Stock-Option Awards (Detail) (USD $)	12 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012	Dec. 25, 2011
Shares
Outstanding at beginning of year	5,575,401	11,344,018	20,340,291
Granted		22,558	109,699
Exercised	(968,891)	(1,598,902)	(2,716,637)
Canceled/Expired	(1,599,852)	(4,192,273)	(6,389,335)
Outstanding at end of year	3,006,658	5,575,401	11,344,018	20,340,291
Options exercisable at year end	2,818,658	4,574,619	8,942,897
Weighted average grant date fair value of options granted during the year		$ 8.20	$ 5.43
Weighted average exercise price
Outstanding at beginning of year	$ 29.76	$ 43.50	$ 47.66
Granted		$ 20.48	$ 14.33
Exercised	$ 14.47	$ 13.44	$ 9.38
Canceled/Expired	$ 53.89	$ 73.11	$ 70.76
Outstanding at end of year	$ 21.84	$ 29.76	$ 43.50	$ 47.66
Options exercisable at year end	$ 22.23	$ 32.85	$ 51.35
Weighted average remaining contractual term
Outstanding at beginning of year	2 years 9 months 18 days	3 years 2 months 12 days	3 years 2 months 12 days	3 years 6 months 2 days
Outstanding at end of year	2 years 9 months 18 days	3 years 2 months 12 days	3 years 2 months 12 days	3 years 6 months 2 days
Options exercisable at year end	2 years 8 months 0 days	2 years 9 months 18 days	2 years 7 months 6 days
Aggregate intrinsic value
Outstanding at beginning of year	$ 46,988,804	$ 16,902,892	$ 17,184,761
Outstanding at end of year	37,497,113	46,988,804	16,902,892	17,184,761
Options exercisable at year end	$ 34,543,513	$ 33,348,296	$ 8,845,944