Employee Benefits (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 24, 2011	Sep. 25, 2010	Sep. 24, 2011	Sep. 25, 2010
Employee benefits
Expected contributions during the current fiscal year	$ 10,666		$ 10,666
Pension Benefits
Employee benefits
Service cost	758	793	2,279	1,906
Interest cost	3,016	2,903	9,056	8,398
Expected return on plan assets	(3,407)	(3,165)	(10,213)	(9,295)
Amortization of prior service cost	(155)	(148)	(466)	(447)
Amortization of net loss (gain)	239	178	693	534
Net periodic benefit cost	451	561	1,349	1,096
Company contributions	1,100	1,913	7,119	5,536
Supplemental Retirement Benefits
Employee benefits
Service cost	159	149	477	447
Interest cost	300	335	901	1,005
Amortization of prior service cost	125	124	374	374
Amortization of net loss (gain)	53	38	158	114
Net periodic benefit cost	$ 637	$ 646	$ 1,910	$ 1,940