Supplemental Stockholders' Equity Information - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	$ 1,059,814	$ 958,077	$ 1,042,641	$ 897,363
Income tax (benefit)/expense	2,015	684	3,414	3,504
Other comprehensive income, net of tax	5,818	2,041	9,740	9,883
Balance, end of period	1,085,203	979,691	1,085,203	979,691
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period			4,677
Other comprehensive (loss)/income before reclassifications, before tax			(127)
Amounts reclassified from accumulated other comprehensive loss, before tax			0
Income tax (benefit)/expense			(33)
Other comprehensive income, net of tax			(94)
Balance, end of period	4,583		4,583
Funded Status of Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period			(520,308)
Other comprehensive (loss)/income before reclassifications, before tax			0
Amounts reclassified from accumulated other comprehensive loss, before tax			9,792
Income tax (benefit)/expense			2,535
Other comprehensive income, net of tax			7,257
Balance, end of period	(513,051)		(513,051)
Net unrealized Loss on available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period			(2,093)
Other comprehensive (loss)/income before reclassifications, before tax			3,489
Amounts reclassified from accumulated other comprehensive loss, before tax			0
Income tax (benefit)/expense			912
Other comprehensive income, net of tax			2,577
Balance, end of period	484		484
Parent
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	1,057,954	957,991	1,040,781	897,279
Other comprehensive (loss)/income before reclassifications, before tax			3,362
Amounts reclassified from accumulated other comprehensive loss, before tax			9,792
Income tax (benefit)/expense			3,414
Other comprehensive income, net of tax	5,818	2,041	9,740	9,883
Balance, end of period	1,083,343	979,606	1,083,343	979,606
Accumulated Other Comprehensive Loss, Net of Income Taxes
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(513,802)	(509,322)	(517,724)	(423,029)
Other comprehensive income, net of tax	5,818	2,041	9,740	9,883
Balance, end of period	$ (507,984)	$ (507,281)	$ (507,984)	$ (507,281)