Pension and Other Postretirement Obligations - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2021	Jun. 28, 2020	Jul. 04, 2021	Jun. 28, 2020
Pension Obligations
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,155	$ 892	$ 2,041	$ 1,824
Interest cost	1,897	2,410	3,703	4,747
Expected return on plan assets	(4,527)	(4,004)	(8,195)	(7,944)
Amortization of prior service cost	28	45	56	89
Actuarial losses (gains)	976	673	1,955	1,350
Net periodic benefit cost (benefit)	(471)	16	(440)	66
Other Postretirement Obligations
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	8	18	16
Interest cost	186	195	363	397
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Actuarial losses (gains)	(5)	(19)	(11)	(38)
Net periodic benefit cost (benefit)	$ 190	$ 184	$ 370	$ 375