Pension Benefits - Net Periodic Pension Cost (Details) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 25, 2016 USD ($)	Jun. 26, 2016 USD ($)	Sep. 27, 2015 USD ($)	Mar. 29, 2015 USD ($)	Sep. 25, 2016 USD ($) plan	Sep. 27, 2015 USD ($)
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 (income)/expense	(4,971)	$ 11,700	0	4,700	6,730	4,697
Qualified Plans
Pension Benefits
Service cost	2,248		2,989		6,743	8,964
Interest cost	16,573		18,514		49,720	55,966
Expected return on plan assets	(27,790)		(28,832)		(83,369)	(86,439)
Amortization of actuarial loss	7,069		9,478		21,206	28,354
Amortization of prior service credit	(487)		(487)		(1,459)	(1,459)
Effect of settlement					0	40,329
Net periodic postretirement benefit income	(2,387)		1,662		(7,159)	45,715
Non-Qualified Plans
Pension Benefits
Service cost	0		0		0	0
Interest cost	2,034		2,502		6,102	7,506
Expected return on plan assets	0		0		0	0
Amortization of actuarial loss	1,054		1,271		3,160	3,811
Amortization of prior service credit	0		0		0	0
Effect of settlement					0	0
Net periodic postretirement benefit income	3,088		3,773		9,262	11,317
Pension Plans, Defined Benefit
Pension Benefits
Service cost	2,248		2,989		6,743	8,964
Interest cost	18,607		21,016		55,822	63,472
Expected return on plan assets	(27,790)		(28,832)		(83,369)	(86,439)
Amortization of actuarial loss	8,123		10,749		24,366	32,165
Amortization of prior service credit	(487)		(487)		(1,459)	(1,459)
Effect of settlement					0	40,329
Net periodic postretirement benefit income	$ 701		$ 5,435		2,103	57,032
Pension contributions					6,000	$ 5,300
Expected contributions in 2016					$ 7,800
Pension settlement charges				40,300
Pension obligation reduction				$ 142,800