Benefit Plans - Net Periodic Postretirement Benefit Cost (Detail) - Postretirement Benefits [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2015	Jun. 29, 2014	Jun. 28, 2015	Jun. 29, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 325	$ 383	$ 650	$ 766
Interest cost	707	825	1,415	1,650
Recognized net actuarial loss	718	563	1,435	1,126
Amortization of prior service cost	(840)	(378)	(1,680)	(756)
Net periodic pension cost (benefit)	$ 910	$ 1,393	$ 1,820	$ 2,786