RESTRUCTURING ACTIVITIES - Restructuring Activities - Restruciting Expenses and Related Costs (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 29, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 4,400
ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3,628
Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	772
Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,340
Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,568	$ 23,515
Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	772
Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,060
Selling, General and Administrative Expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,060	$ 18,460
Selling, General and Administrative Expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0
Severance | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	423
Severance | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	423
Severance | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0
Severance | Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,978
Severance | Selling, General and Administrative Expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,978
Severance | Selling, General and Administrative Expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0
Other cash restructuring expenses | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	772
Other cash restructuring expenses | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0
Other cash restructuring expenses | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	772
Other cash restructuring expenses | Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	82
Other cash restructuring expenses | Selling, General and Administrative Expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	82
Other cash restructuring expenses | Selling, General and Administrative Expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0
Asset impairments/net loss on disposals | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,145
Asset impairments/net loss on disposals | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,145
Asset impairments/net loss on disposals | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0