Pension and Postretirement Benefit Obligations - Components of Net Periodic Postretirement Benefit Cost (Detail) - Net Postretirement Benefits Activity [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 389	$ 503	$ 778	$ 1,005
Interest cost	693	696	1,386	1,392
Recognized net actuarial loss	195	499	391	998
Amortization of prior service cost	(322)	(462)	(646)	(924)
Net periodic benefit cost	$ 955	$ 1,236	$ 1,909	$ 2,471