Pension Benefits - Net Periodic Pension Cost (Details) $ in Thousands	3 Months Ended
	Mar. 27, 2016 USD ($) plan	Mar. 29, 2015 USD ($)
Pension Benefits
Number of joint Company and Guild-sponsored defined benefit plans | plan	2
Pension settlement charges	$ 0	$ 40,329
Lump-sum payments for pension settlement		98,300
Multiemployer pension plan withdrawal expense	0	4,697
Qualified Plans
Pension Benefits
Service cost	2,247	2,988
Interest cost	16,574	18,938
Expected return on plan assets	(27,790)	(28,775)
Amortization of actuarial loss	7,069	9,397
Amortization of prior service credit	(486)	(486)
Effect of settlement	0	40,329
Net periodic (income)/cost	(2,386)	42,391
Non-Qualified Plans
Pension Benefits
Service cost	0	0
Interest cost	2,034	2,502
Expected return on plan assets	0	0
Amortization of actuarial loss	1,053	1,270
Amortization of prior service credit	0	0
Effect of settlement	0	0
Net periodic (income)/cost	3,087	3,772
Pension Plans, Defined Benefit
Pension Benefits
Service cost	2,247	2,988
Interest cost	18,608	21,440
Expected return on plan assets	(27,790)	(28,775)
Amortization of actuarial loss	8,122	10,667
Amortization of prior service credit	(486)	(486)
Effect of settlement	0	40,329
Net periodic (income)/cost	701	46,163
Pension Contributions	2,100	2,100
Expected contributions in 2016	$ 7,600
Pension settlement charges		40,300
Pension obligation reduction		$ (142,800)