Supplemental Stockholders' Equity Information - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Apr. 01, 2018	Sep. 24, 2017	Sep. 30, 2018	Sep. 24, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period		$ 897,363		$ 897,363	$ 844,244
Income tax expense/(benefit)	$ 2,031		$ 4,200	5,535	11,557
Other comprehensive income, net of tax	5,725		7,739	15,608	19,294
AOCI reclassification to Retained Earnings		(94,100)
Balance, end of period	1,006,671		918,674	1,006,671	918,674
Curtailment recorded		2,600
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period		6,328		6,328
Other comprehensive (loss)/income before reclassifications, before tax				(2,923)
Amounts reclassified from accumulated other comprehensive loss, before tax				0
Income tax expense/(benefit)				(764)
Other comprehensive income, net of tax				(2,159)
AOCI reclassification to Retained Earnings				1,576
Balance, end of period	5,745			5,745
Funded Status of Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period		(427,819)		(427,819)
Other comprehensive (loss)/income before reclassifications, before tax				3,103
Amounts reclassified from accumulated other comprehensive loss, before tax				21,747
Income tax expense/(benefit)				6,504
Other comprehensive income, net of tax				18,346
AOCI reclassification to Retained Earnings				(95,378)
Balance, end of period	(504,851)			(504,851)
Net unrealized Loss on available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period		(1,538)		(1,538)
Other comprehensive (loss)/income before reclassifications, before tax				(784)
Amounts reclassified from accumulated other comprehensive loss, before tax				0
Income tax expense/(benefit)				(205)
Other comprehensive income, net of tax				(579)
AOCI reclassification to Retained Earnings				(333)
Balance, end of period	(2,450)			(2,450)
Parent
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period		897,279		897,279	847,815
Other comprehensive (loss)/income before reclassifications, before tax				(604)
Amounts reclassified from accumulated other comprehensive loss, before tax				21,747
Income tax expense/(benefit)				5,535
Other comprehensive income, net of tax				15,608	19,294
AOCI reclassification to Retained Earnings				(94,135)
Balance, end of period	1,006,588		918,678	1,006,588	918,678
Accumulated Other Comprehensive Loss, Net of Income Taxes
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period		$ (423,029)		(423,029)	(479,816)
Other comprehensive income, net of tax				15,608	19,294
Balance, end of period	$ (501,556)		$ (460,522)	$ (501,556)	$ (460,522)