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SEGMENT AND GEOGRAPHICAL INFORMATION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 03, 2026	Apr. 04, 2025
Revenue
Revenue	$ 155,114	$ 152,386
United States
Revenue
Revenue	155,114	152,386
Commercial
Revenue
Revenue	21,235	15,326
Government
Revenue
Revenue	69,036	72,596
Utilities
Revenue
Revenue	64,843	64,464
Time-and-materials
Revenue
Revenue	30,900	29,662
Unit-based
Revenue
Revenue	56,670	53,962
Fixed price
Revenue
Revenue	67,544	68,762
Energy
Revenue
Revenue	127,968	126,248
Energy | United States
Revenue
Revenue	127,968	126,248
Energy | Commercial
Revenue
Revenue	19,389	13,515
Energy | Government
Revenue
Revenue	43,846	48,324
Energy | Utilities
Revenue
Revenue	64,733	64,409
Energy | Time-and-materials
Revenue
Revenue	12,700	11,602
Energy | Unit-based
Revenue
Revenue	49,617	47,707
Energy | Fixed price
Revenue
Revenue	65,651	66,939
Engineering and Consulting
Revenue
Revenue	27,146	26,138
Engineering and Consulting | United States
Revenue
Revenue	27,146	26,138
Engineering and Consulting | Commercial
Revenue
Revenue	1,846	1,811
Engineering and Consulting | Government
Revenue
Revenue	25,190	24,272
Engineering and Consulting | Utilities
Revenue
Revenue	110	55
Engineering and Consulting | Time-and-materials
Revenue
Revenue	18,200	18,060
Engineering and Consulting | Unit-based
Revenue
Revenue	7,053	6,255
Engineering and Consulting | Fixed price
Revenue
Revenue	$ 1,893	$ 1,823

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