Pension and Other Postretirement Benefits - Net Periodic Pension Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Pension Benefits
Service cost	$ 1,279	$ 2,553	$ 2,557	$ 5,200
Interest cost	16,796	15,054	33,593	30,052
Expected return on plan assets	(20,259)	(20,591)	(40,517)	(41,145)
Amortization of actuarial loss	5,729	7,974	11,458	16,030
Amortization of prior service credit	(486)	(486)	(972)	(972)
Net periodic postretirement benefit income	3,059	4,504	6,119	9,165
Qualified Plans
Pension Benefits
Service cost	1,279	2,553	2,557	5,200
Interest cost	14,708	13,206	29,417	26,357
Expected return on plan assets	(20,259)	(20,591)	(40,517)	(41,145)
Amortization of actuarial loss	4,635	6,680	9,270	13,442
Amortization of prior service credit	(486)	(486)	(972)	(972)
Net periodic postretirement benefit income	(123)	1,362	(245)	2,882
Pension contributions			4,300	4,200
Expected contributions in 2018	9,000		9,000
Non- Qualified Plans
Pension Benefits
Service cost	0	0	0	0
Interest cost	2,088	1,848	4,176	3,695
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss	1,094	1,294	2,188	2,588
Amortization of prior service credit	0	0	0	0
Net periodic postretirement benefit income	$ 3,182	$ 3,142	$ 6,364	$ 6,283