Pension Benefits - Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Details) - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2019	Dec. 30, 2018	Dec. 31, 2017
Pension Benefits
Net actuarial (gain)/loss	$ (10,292)	$ 29,965	$ 22,600
Prior service cost	706	0	0
Amortization of loss	(23,020)	(31,916)	(33,369)
Amortization of prior service credit	1,932	1,945	1,945
Effect of settlement	0	(421)	(102,109)
Total recognized in other comprehensive income	(30,674)	(427)	(110,933)
Net periodic pension cost	12,324	18,083	109,014
Total recognized in net periodic benefit (income)/cost and other comprehensive (income)/loss	(18,350)	17,656	(1,919)
Estimated actuarial loss that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	29,000
Estimated prior service credit that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	2,000
Defined contribution plan, cost recognized	$ 27,000	$ 22,000	$ 23,000