Pension and Other Postretirement Benefits - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2019	Sep. 30, 2018	Sep. 29, 2019	Sep. 30, 2018
Pension Benefits
Gain from pension liability adjustment	$ 2,045	$ 4,851	$ 2,045	$ 4,851
Pension Plan
Pension Benefits
Service cost	1,278	2,393	3,835	7,593
Interest cost	16,797	15,055	50,390	45,107
Expected return on plan assets	(20,258)	(20,591)	(60,775)	(61,736)
Amortization of actuarial loss	5,729	7,974	17,187	24,004
Amortization of prior service credit	(487)	(487)	(1,459)	(1,459)
Other	0	421	0	421
Net periodic postretirement benefit income	3,059	4,765	9,178	13,930
Qualified Plans | Pension Plan
Pension Benefits
Service cost	1,278	2,393	3,835	7,593
Interest cost	14,708	13,207	44,125	39,564
Expected return on plan assets	(20,258)	(20,591)	(60,775)	(61,736)
Amortization of actuarial loss	4,635	6,680	13,905	20,122
Amortization of prior service credit	(487)	(487)	(1,459)	(1,459)
Other	0	0	0	0
Net periodic postretirement benefit income	(124)	1,202	(369)	4,084
Pension contributions			6,300	6,200
Expected contributions in 2018	9,000		9,000
Non- Qualified Plans | Pension Plan
Pension Benefits
Service cost	0	0	0	0
Interest cost	2,089	1,848	6,265	5,543
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss	1,094	1,294	3,282	3,882
Amortization of prior service credit	0	0	0	0
Other	0	421	0	421
Net periodic postretirement benefit income	$ 3,183	$ 3,563	$ 9,547	$ 9,846