RESTRUCTURING ACTIVITIES - Restructuring Activities - Restruciting Expenses and Related Costs (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 7,019	$ 11,419
ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5,419	9,047
Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,474	2,246
Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	126	126
Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	4,490	6,830
Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3,016	4,584
Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,474	2,246
Total cost of sales | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,529	4,589
Selling, General and Administrative Expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,403	4,463
Selling, General and Administrative Expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Selling, General and Administrative Expenses | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	126	126
Severance | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,118	2,541
Severance | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,603	2,026
Severance | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	515	515
Severance | Total cost of sales | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Severance | Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,533	3,511
Severance | Selling, General and Administrative Expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,533	3,511
Severance | Selling, General and Administrative Expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Severance | Selling, General and Administrative Expenses | Corporate Segment [Member]
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	1,111	1,883
Other cash restructuring expenses | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	152	152
Other cash restructuring expenses | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	959	1,731
Other cash restructuring expenses | Total cost of sales | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Other cash restructuring expenses | Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	611	693
Other cash restructuring expenses | Selling, General and Administrative Expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	485	567
Other cash restructuring expenses | Selling, General and Administrative Expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Other cash restructuring expenses | Selling, General and Administrative Expenses | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	126	126
Asset impairments/net loss on disposals | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,261	2,406
Asset impairments/net loss on disposals | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,261	2,406
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 Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Asset impairments/net loss on disposals | Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges	385	385
Asset impairments/net loss on disposals | Selling, General and Administrative Expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	385	385
Asset impairments/net loss on disposals | Selling, General and Administrative Expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Asset impairments/net loss on disposals | Selling, General and Administrative Expenses | Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0	$ 0