Pension Benefits - Net Periodic Pension Cost (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 26, 2016 USD ($)	Jun. 28, 2015 USD ($)	Mar. 29, 2015 USD ($)	Jun. 26, 2016 USD ($) plan	Jun. 28, 2015 USD ($)
Pension Benefits
Number of joint Company and Guild-sponsored defined benefit plans | plan				2
Pension settlement charges	$ 0	$ 0		$ 0	$ 40,329
Lump-sum payments for pension settlement			$ 98,300
Multiemployer pension plan withdrawal expense	11,701	0	4,697	11,701	4,697
Qualified Plans
Pension Benefits
Service cost	2,248	2,987		4,495	5,975
Interest cost	16,573	18,514		33,147	37,452
Expected return on plan assets	(27,789)	(28,832)		(55,579)	(57,607)
Amortization of actuarial loss	7,068	9,479		14,137	18,876
Amortization of prior service credit	(486)	(486)		(972)	(972)
Effect of settlement				0	40,329
Net periodic postretirement benefit income	(2,386)	1,662		(4,772)	44,053
Non-Qualified Plans
Pension Benefits
Service cost	0	0		0	0
Interest cost	2,034	2,502		4,068	5,004
Expected return on plan assets	0	0		0	0
Amortization of actuarial loss	1,053	1,270		2,106	2,540
Amortization of prior service credit	0	0		0	0
Effect of settlement				0	0
Net periodic postretirement benefit income	3,087	3,772		6,174	7,544
Pension Plans, Defined Benefit
Pension Benefits
Service cost	2,248	2,987		4,495	5,975
Interest cost	18,607	21,016		37,215	42,456
Expected return on plan assets	(27,789)	(28,832)		(55,579)	(57,607)
Amortization of actuarial loss	8,121	10,749		16,243	21,416
Amortization of prior service credit	(486)	(486)		(972)	(972)
Effect of settlement				0	40,329
Net periodic postretirement benefit income	$ 701	$ 5,434		1,402	51,597
Pension contributions				3,900	$ 3,200
Expected contributions in 2016				$ 7,600
Pension settlement charges			40,300
Pension obligation reduction			$ 142,800