Components of Net Periodic Pension and Other Postretirement Benefit Costs (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 25, 2011	Jun. 30, 2012	Jun. 25, 2011
Pension Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 927	$ 634	$ 1,870	$ 1,273
Interest cost	16,186	17,546	32,344	35,088
Expected return on plan assets	(20,774)	(20,098)	(41,547)	(40,203)
Recognized actuarial loss	4,486	4,325	8,977	8,752
Net periodic benefit cost (income)	825	2,407	1,644	4,910
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	72	18	144	115
Interest cost	230	207	466	507
Recognized actuarial loss	45	26	101	110
Amortization of prior service credits	(1,001)	(1,002)	(2,004)	(2,004)
Net periodic benefit cost (income)	$ (654)	$ (751)	$ (1,293)	$ (1,272)