Income Taxes - Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 25, 2016	Dec. 27, 2015
Deferred tax assets
Retirement, postemployment and deferred compensation plans	$ 275,611	$ 309,711
Accruals for other employee benefits, compensation, insurance and other	34,466	32,731
Accounts receivable allowances	2,450	1,690
Net operating losses	2,598	38,703
Investment in joint ventures	5,329	0
Other	39,943	44,099
Gross deferred tax assets	360,397	426,934
Valuation allowance	0	(36,204)
Net deferred tax assets	360,397	390,730
Deferred tax liabilities
Property, plant and equipment	46,284	57,065
Intangible assets	11,975	10,790
Investments in joint ventures	0	11,694
Other	796	2,039
Gross deferred tax liabilities	59,055	81,588
Net deferred tax asset	$ 301,342	$ 309,142
Valuation allowance, period for recoverability measurement	3 years