Employee Benefit Plans (Components of Net Periodic Benefit Costs) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 24, 2017	Sep. 30, 2018	Sep. 24, 2017
Pension and SERPA Benefits
Defined Benefit Plan Disclosure
Service cost	$ 8,063	$ 7,896	$ 24,281	$ 23,688
Interest cost	20,729	21,269	62,048	63,807
Expected return on plan assets	(36,925)	(35,345)	(110,742)	(106,035)
Amortization of unrecognized: Prior service cost	(105)	256	(316)	764
Amortization of unrecognized: Net loss	16,318	10,998	48,455	32,994
Curtailment loss	0	0	1,018	0
Net periodic benefit cost	8,080	5,074	24,744	15,218
Postretirement Healthcare Benefits
Defined Benefit Plan Disclosure
Service cost	1,789	1,875	5,390	5,625
Interest cost	2,886	3,412	8,669	10,236
Expected return on plan assets	(3,541)	(3,156)	(10,623)	(9,468)
Amortization of unrecognized: Prior service cost	(460)	(543)	(1,380)	(1,629)
Amortization of unrecognized: Net loss	454	815	1,362	2,445
Net periodic benefit cost	$ 1,128	$ 2,403	$ 3,418	$ 7,209