SEGMENT AND GEOGRAPHICAL INFORMATION (Details) $ in Thousands	3 Months Ended
	Apr. 03, 2020 USD ($) segment	Mar. 29, 2019 USD ($)	Dec. 27, 2019 USD ($)
SEGMENT INFORMATION
Number of operating segments | segment	2
Number of reporting segments | segment	2
Segment reconciliation
Contract revenue	$ 106,026	$ 91,793
Depreciation and amortization	4,519	2,654
Interest expense	1,513	(1,121)
Segment profit (loss) before income tax expense	(9,759)	(1,344)
Income tax expense (benefit)	(1,605)	(927)
Net income (loss)	(8,154)	(417)
Segment assets(1)	412,803	320,364	$ 439,913
Energy
Segment reconciliation
Contract revenue	87,799	74,692
Engineering and Consulting
Segment reconciliation
Contract revenue	18,227	17,101
Reporting Segments | Energy
Segment reconciliation
Contract revenue	87,799	74,692
Depreciation and amortization	4,236	2,370
Interest expense	11	(447)
Segment profit (loss) before income tax expense	(6,406)	(1,487)
Income tax expense (benefit)	(1,054)	(1,026)
Net income (loss)	(5,353)	(461)
Segment assets(1)	355,856	189,739
Reporting Segments | Engineering and Consulting
Segment reconciliation
Contract revenue	18,227	17,101
Depreciation and amortization	283	284
Interest expense		(674)
Segment profit (loss) before income tax expense	2,004	1,605
Income tax expense (benefit)	330	1,107
Net income (loss)	1,676	498
Segment assets(1)	24,866	22,355
Unallocated Corporate
Segment reconciliation
Interest expense	1,502
Segment profit (loss) before income tax expense	(5,357)	(1,462)
Income tax expense (benefit)	(881)	(1,008)
Net income (loss)	(4,477)	(454)
Segment assets(1)	55,211	131,400
Intersegment
Segment reconciliation
Contract revenue	0	0
Segment assets(1)	$ (23,130)	$ (23,130)