RESTRUCTURING ACTIVITIES - Restructuring Activities - Restructuring Expenses and Related Costs (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 29, 2018	Sep. 29, 2018	Dec. 29, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 6,243	$ 17,662
ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5,746	14,793
Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	497	2,743
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	126
Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3,935	10,765
Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3,438	8,022	$ 18,380
Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	497	2,743
Total cost of sales | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Total selling, general and administrative expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,308	6,897
Total selling, general and administrative expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,308	6,771	$ 15,651
Total selling, general and administrative expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Total selling, general and administrative expenses | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	126
Severance | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,706	4,247
Severance | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,706	3,732
Severance | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	515
Severance | Total cost of sales | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Severance | Total selling, general and administrative expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,757	5,268
Severance | Total selling, general and administrative expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,757	5,268
Severance | Total selling, general and administrative expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Severance | Total selling, general and administrative expenses | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Other cash restructuring expenses | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	823	2,706
Other cash restructuring expenses | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	326	478
Other cash restructuring expenses | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	497	2,228
Other cash restructuring expenses | Total cost of sales | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Other cash restructuring expenses | Total selling, general and administrative expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	551	1,244
Other cash restructuring expenses | Total selling, general and administrative expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	551	1,118
Other cash restructuring expenses | Total selling, general and administrative expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Other cash restructuring expenses | Total selling, general and administrative expenses | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	126
Asset impairments/net loss on disposals | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,406	3,812
Asset impairments/net loss on disposals | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,406	3,812
Asset impairments/net loss on disposals | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Asset impairments/net loss on disposals | Total cost of sales | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Asset impairments/net loss on disposals | Total selling, general and administrative expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	385
Asset impairments/net loss on disposals | Total selling, general and administrative expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	385
Asset impairments/net loss on disposals | Total selling, general and administrative expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Asset impairments/net loss on disposals | Total selling, general and administrative expenses | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0	$ 0