Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 643,303	$ 695,607	$ 1,260,556	$ 1,369,091
Operating income	34,295	26,159	41,753	40,511
Amortization of intangible assets	8,047	8,196	16,094	16,853
Corporate
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Operating income	(4,967)	(3,091)	(14,479)	(13,743)
Amortization of intangible assets	0	0	0	0
GMS | Operating Segments
Segment Reporting Information [Line Items]
Revenues	507,854	526,025	965,298	1,030,504
Operating income	31,537	25,276	44,140	51,067
Amortization of intangible assets	4,115	4,140	8,231	8,399
NSS | Operating Segments
Segment Reporting Information [Line Items]
Revenues	135,449	169,582	295,258	338,587
Operating income	7,725	3,974	12,092	3,187
Amortization of intangible assets	$ 3,932	$ 4,056	$ 7,863	$ 8,454