SEGMENT AND GEOGRAPHICAL INFORMATION - Concentration Risk (Details)	12 Months Ended
	Dec. 29, 2023	Dec. 30, 2022	Dec. 31, 2021
Revenue from Contract with Customer Benchmark | Customer Concentration Risk | Top Ten Customers
Concentration Risk
Concentration risk (as a percent)	52.70%	54.60%	49.20%
Revenue from Contract with Customer Benchmark | Customer Concentration Risk | Los Angeles Department of Water and Power
Concentration Risk
Concentration risk (as a percent)		12.00%	10.80%
Revenue from Contract with Customer Benchmark | Geographic Concentration Risk | California
Concentration Risk
Concentration risk (as a percent)	45.10%	41.70%	36.80%
Revenue from Contract with Customer Benchmark | Geographic Concentration Risk | New York
Concentration Risk
Concentration risk (as a percent)	24.70%	22.80%	21.00%
Revenue from Contract with Customer, Segment Benchmark | Customer Concentration Risk | Los Angeles Department of Water and Power | Energy
Concentration Risk
Concentration risk (as a percent)		14.40%
Revenue from Contract with Customer, Segment Benchmark | Customer Concentration Risk | Los Angeles Department of Water and Power, Duke Energy, and Consolidated Edison of New York | Engineering and Consulting
Concentration Risk
Concentration risk (as a percent)			34.50%
Revenue from Contract with Customer, Segment Benchmark | Customer Concentration Risk | Los Angeles Department of Water and Power, and The Dormitory Authority State of New York | Energy
Concentration Risk
Concentration risk (as a percent)	22.70%
Revenue from Contract with Customer, Segment Benchmark | Customer Concentration Risk | City of Elk Grove | Engineering and Consulting
Concentration Risk
Concentration risk (as a percent)			10.30%