Pension and Other Postretirement Obligations - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 29, 2020	Mar. 31, 2019
Pension Obligations
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 932	$ 1,007
Interest cost	2,337	2,960
Expected return on plan assets	(3,940)	(4,116)
Amortization of prior service cost (credit)	44	(14)
Actuarial losses (gains)	677	321
Net periodic benefit cost	50	158
Other Postretirement Obligations
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	10
Interest cost	202	272
Expected return on plan assets	0	0
Amortization of prior service cost (credit)	0	0
Actuarial losses (gains)	(19)	(26)
Net periodic benefit cost	$ 191	$ 256