Pension Benefits - Net Periodic Pension Cost (Details) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 27, 2015 USD ($)	Mar. 29, 2015 USD ($)	Sep. 28, 2014 USD ($)	Jun. 29, 2014 USD ($)	Sep. 27, 2015 USD ($) plan	Sep. 28, 2014 USD ($)
Pension Benefits
Number of single employer defined benefit plans | plan					2
Pension settlement charges	$ 0		$ 0		$ 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	2,989		2,386		8,964	7,158
Interest cost	18,514		21,112		55,966	63,336
Expected return on plan assets	(28,832)		(28,460)		(86,439)	(85,380)
Amortization of actuarial loss	9,478		6,655		28,354	19,964
Amortization of prior service credit	(487)		(486)		(1,459)	(1,456)
Effect of settlement					40,329	0
Net periodic pension cost	1,662		1,207		45,715	3,622
Non-Qualified Plans
Pension Benefits
Service cost	0		0		0	0
Interest cost	2,502		2,382		7,506	7,968
Expected return on plan assets	0		0		0	0
Amortization of actuarial loss	1,271		990		3,811	3,077
Amortization of prior service credit	0		0		0	0
Effect of settlement					0	9,525
Net periodic pension cost	3,773		3,372		11,317	20,570
Pension Plans, Defined Benefit
Pension Benefits
Service cost	2,989		2,386		8,964	7,158
Interest cost	21,016		23,494		63,472	71,304
Expected return on plan assets	(28,832)		(28,460)		(86,439)	(85,380)
Amortization of actuarial loss	10,749		7,645		32,165	23,041
Amortization of prior service credit	(487)		(486)		(1,459)	(1,456)
Effect of settlement					40,329	9,525
Net periodic pension cost	$ 5,435		$ 4,579		57,032	24,192
Pension Contributions					5,300	$ 12,500
Estimated future employer contributions in 2015					$ 7,700
Pension settlement charges		40,300		9,500
Lump-sum payments to be made from plan assets		98,300
Pension obligation reduction		$ (142,800)		$ (32,000)