Income Taxes - Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 25, 2016
Deferred tax assets
Retirement, postemployment and deferred compensation plans	$ 140,657	$ 275,611
Accruals for other employee benefits, compensation, insurance and other	16,883	34,466
Accounts receivable allowances	1,391	2,450
Net operating losses	6,228	2,598
Investment in joint ventures	0	5,329
Other	30,295	39,943
Gross deferred tax assets	195,454	360,397
Deferred tax liabilities
Property, plant and equipment	31,043	46,284
Intangible assets	7,300	11,975
Investments in joint ventures	615	0
Other	3,450	796
Gross deferred tax liabilities	42,408	59,055
Net deferred tax asset	$ 153,046	$ 301,342
Valuation allowance, period for recoverability measurement	3 years