SEGMENT AND GEOGRAPHICAL INFORMATION - Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Apr. 01, 2022
Segment reconciliation
Contract revenue	$ 102,603	$ 91,838
Depreciation and amortization	4,200	4,409
Interest expense, net	2,466	751
Segment profit (loss) before income tax expense	1,688	(6,162)
Income tax expense (benefit)	756	(2,389)
Net income (loss)	932	(3,773)
Energy
Segment reconciliation
Contract revenue	83,285	74,886
Depreciation and amortization	3,924	4,157
Engineering and Consulting
Segment reconciliation
Contract revenue	19,318	16,952
Depreciation and amortization	276	252
Operating Segments | Energy
Segment reconciliation
Interest expense, net	2	4
Segment profit (loss) before income tax expense	2,771	(4,353)
Income tax expense (benefit)	1,241	(1,687)
Net income (loss)	1,530	(2,665)
Operating Segments | Engineering and Consulting
Segment reconciliation
Segment profit (loss) before income tax expense	2,587	2,107
Income tax expense (benefit)	1,158	817
Net income (loss)	1,428	1,290
Corporate, Non-Segment
Segment reconciliation
Interest expense, net	2,464	747
Segment profit (loss) before income tax expense	(3,670)	(3,916)
Income tax expense (benefit)	(1,643)	(1,519)
Net income (loss)	$ (2,026)	$ (2,398)