Pension Benefits - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 28, 2015	Mar. 29, 2015	Jun. 29, 2014	Jun. 28, 2015	Jun. 29, 2014
Pension Benefits
Pension settlement charges	$ 0		$ 9,525	$ 40,329	$ 9,525
Lump-sum payments for pension settlement			24,000
Multiemployer pension plan withdrawal expense	0	$ 4,700	0	4,697	0
Qualified Plans
Pension Benefits
Service cost	2,987		2,385	5,975	4,772
Interest cost	18,514		21,112	37,452	42,224
Expected return on plan assets	(28,832)		(28,460)	(57,607)	(56,920)
Amortization of actuarial loss	9,479		6,711	18,876	13,309
Amortization of prior service (credit)	(486)		(484)	(972)	(970)
Effect of settlement	0		0	40,329	0
Net periodic pension cost/postretirement benefit expense	1,662		1,264	44,053	2,415
Non-Qualified Plans
Pension Benefits
Service cost	0		0	0	0
Interest cost	2,502		2,711	5,004	5,586
Expected return on plan assets	0		0	0	0
Amortization of actuarial loss	1,270		1,033	2,540	2,087
Amortization of prior service (credit)	0		0	0	0
Effect of settlement	0		9,525	0	9,525
Net periodic pension cost/postretirement benefit expense	3,772		13,269	7,544	17,198
Pension Plans, Defined Benefit
Pension Benefits
Service cost	2,987		2,385	5,975	4,772
Interest cost	21,016		23,823	42,456	47,810
Expected return on plan assets	(28,832)		(28,460)	(57,607)	(56,920)
Amortization of actuarial loss	10,749		7,744	21,416	15,396
Amortization of prior service (credit)	(486)		(484)	(972)	(970)
Effect of settlement	0		9,525	40,329	9,525
Net periodic pension cost/postretirement benefit expense	5,434		14,533	51,597	19,613
Pension Contributions				3,200	$ 9,100
Estimated future employer contributions in 2015				8,000
Pension settlement charges		40,300	$ 9,500
Lump-sum payments to be made from plan assets		98,300
Pension obligation reduction	$ (32,000)	$ (142,800)		$ (32,000)