Segment Information - Summary of Segment Information (Details) - USD ($)	3 Months Ended
	Apr. 03, 2021	Mar. 28, 2020
Segment Reporting Information [Line Items]
Revenue	$ 417,160,000	$ 355,223,000
Cost of revenue, excluding depreciation and amortization	285,477,000	247,682,000
Gross margin	$ 131,683,000	$ 107,541,000
Gross margin percentage	31.60%	30.30%
Segment Reconciliation:
Total segment gross margin	$ 131,683,000	$ 107,541,000
Branch and regional administrative expenses	69,372,000	59,694,000
Corporate expenses	27,399,000	25,797,000
Depreciation and amortization	4,848,000	4,183,000
Acquisition-related costs	1,768,000	0
Operating income	28,296,000	17,867,000
Interest income	77,000	46,000
Interest expense	(22,425,000)	(21,063,000)
Gain on debt extinguishment		127,000
Other income	159,000	41,791,000
Income before income taxes	6,107,000	38,768,000
PDS
Segment Reporting Information [Line Items]
Revenue	350,827,000	320,513,000
Cost of revenue, excluding depreciation and amortization	248,997,000	227,963,000
Gross margin	$ 101,830,000	$ 92,550,000
Gross margin percentage	29.00%	28.90%
Segment Reconciliation:
Total segment gross margin	$ 101,830,000	$ 92,550,000
HHH
Segment Reporting Information [Line Items]
Revenue	31,518,000	4,477,000
Cost of revenue, excluding depreciation and amortization	17,329,000	2,803,000
Gross margin	$ 14,189,000	$ 1,674,000
Gross margin percentage	45.00%	37.40%
Segment Reconciliation:
Total segment gross margin	$ 14,189,000	$ 1,674,000
MS
Segment Reporting Information [Line Items]
Revenue	34,815,000	30,233,000
Cost of revenue, excluding depreciation and amortization	19,151,000	16,916,000
Gross margin	$ 15,664,000	$ 13,317,000
Gross margin percentage	45.00%	44.00%
Segment Reconciliation:
Total segment gross margin	$ 15,664,000	$ 13,317,000