Pension and Other Postretirement Obligations - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2019	Sep. 30, 2018	Sep. 29, 2019	Sep. 30, 2018
Pension Obligations
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,058	$ 1,717	$ 3,164	$ 3,792
Interest cost	2,921	2,011	8,869	5,792
Expected return on plan assets	(3,842)	(4,660)	(11,977)	(9,688)
Amortization of prior service credit	(143)	(37)	(117)	(59)
Actuarial losses (gains)	327	1,073	969	2,350
Net periodic benefit cost	321	104	908	2,187
Other Postretirement Obligations
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	14	29	40
Interest cost	273	257	815	781
Expected return on plan assets	0	0	0	0
Amortization of prior service credit	0	0	0	0
Actuarial losses (gains)	(25)	0	(76)	0
Net periodic benefit cost	$ 258	$ 271	$ 768	$ 821