Supplemental Stockholders' Equity Information Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 24, 2017	Sep. 25, 2016	Sep. 24, 2017	Sep. 25, 2016	Dec. 25, 2016	Dec. 27, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 918,674	$ 793,171	$ 918,674	$ 793,171	$ 844,244	$ 828,455
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income before reclassifications, before tax			10,089
Amounts reclassified from accumulated other comprehensive loss, before tax			20,762
Income tax expense	4,200	2,912	11,557	8,492
Other comprehensive income, net of tax	7,739	$ 4,244	19,294	$ 13,273
Balance as of September 24, 2017	(460,522)		(460,522)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	5,571		5,571		(1,822)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income before reclassifications, before tax			11,170
Amounts reclassified from accumulated other comprehensive loss, before tax			0
Income tax expense			3,777
Other comprehensive income, net of tax			7,393
Funded Status of Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(465,440)		(465,440)		(477,994)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income before reclassifications, before tax			0
Amounts reclassified from accumulated other comprehensive loss, before tax			20,762
Income tax expense			8,208
Other comprehensive income, net of tax			12,554
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(653)		(653)		0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income before reclassifications, before tax			(1,081)
Amounts reclassified from accumulated other comprehensive loss, before tax			0
Income tax expense			(428)
Other comprehensive income, net of tax			(653)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ (460,522)		$ (460,522)		$ (479,816)