Other Postretirement Benefits - Changes in the Benefit Obligations Recognized in Other Comprehensive Income (Details) (USD $)	12 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Other Postretirement Benefits
Additional postretirement costs	$ 18,000,000	$ 20,000,000	$ 18,000,000
Other Postretirement Benefit Plans, Defined Benefit [Member]
Other Postretirement Benefits
Net actuarial loss/(gain)	8,882,000	(13,500,000)	11,562,000
Prior service credit	(25,489,000)	(1,690,000)	0
Amortization of loss	(4,948,000)	(4,440,000)	(3,328,000)
Amortization of prior service cost	7,199,000	13,051,000	15,112,000
Recognition of prior service credit due to curtailment	0	49,122,000	27,213,000
Total recognized in other comprehensive loss/(income)	(14,356,000)	42,543,000	50,559,000
Net periodic postretirement benefit expense/(income)	4,402,000	(52,543,000)	(33,055,000)
Total recognized in net periodic benefit cost and other comprehensive loss	(9,954,000)	(10,000,000)	17,504,000
Estimated actuarial loss that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	5,300,000
Estimated prior service cost that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	$ 9,700,000