Supplemental Stockholders' Equity Information -Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jul. 01, 2018	Apr. 01, 2018	Jun. 25, 2017	Jul. 01, 2018	Jun. 25, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period		$ 897,363		$ 897,363	$ 844,244
Income tax expense	$ 684		$ 3,826	3,504	7,357
Other comprehensive income, net of tax	2,041		5,990	9,883	11,555
AOCI reclassification to Retained Earnings		(94,100)
Balance, end of period	979,691		884,026	979,691	884,026
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				(2,356)
Amounts reclassified from accumulated other comprehensive loss, before tax				0
Income tax expense				(616)
Other comprehensive income, net of tax				(1,740)
AOCI reclassification to Retained Earnings				1,576
Balance, end of period	6,164			6,164
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				2,597
Amounts reclassified from accumulated other comprehensive loss, before tax				14,244
Income tax expense				4,407
Other comprehensive income, net of tax				12,434
AOCI reclassification to Retained Earnings				(95,378)
Balance, end of period	(510,763)			(510,763)
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				(1,098)
Amounts reclassified from accumulated other comprehensive loss, before tax				0
Income tax expense				(287)
Other comprehensive income, net of tax				(811)
AOCI reclassification to Retained Earnings				(333)
Balance, end of period	(2,682)			(2,682)
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				(857)
Amounts reclassified from accumulated other comprehensive loss, before tax				14,244
Income tax expense				3,504
Other comprehensive income, net of tax				9,883	11,555
AOCI reclassification to Retained Earnings				(94,135)
Balance, end of period	979,606		887,703	979,606	887,703
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				9,883	11,555
Balance, end of period	$ (507,281)		$ (468,261)	$ (507,281)	$ (468,261)