RESTRUCTURING ACTIVITIES - Restructuring Activities - Restructuring Expenses and Related Costs (Details)	3 Months Ended	9 Months Ended
	Sep. 26, 2020 USD ($)	Sep. 26, 2020 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2,910,000	$ 8,489,000
2020 Plan
Restructuring Cost and Reserve [Line Items]
Expected costs of restructuring plan	20,000,000	20,000,000
ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	902,000	2,364,000
Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	579,000	4,253,000
Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,284,000	1,506,000
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	145,000	366,000
Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,673,000	5,348,000
Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	447,000
Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	579,000	3,640,000
Total cost of sales | Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,094,000	1,261,000
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	1,237,000	3,141,000
Total selling, general and administrative expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	902,000	1,917,000
Total selling, general and administrative expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	613,000
Total selling, general and administrative expenses | Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring charges	190,000	245,000
Total selling, general and administrative expenses | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	145,000	366,000
Severance | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	289,000	823,000
Severance | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	399,000
Severance | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Severance | Total cost of sales | Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring charges	289,000	424,000
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	30,000	1,161,000
Severance | Total selling, general and administrative expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	242,000
Severance | Total selling, general and administrative expenses | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	613,000
Severance | Total selling, general and administrative expenses | Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring charges	30,000	85,000
Severance | Total selling, general and administrative expenses | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	221,000
Other cash restructuring expenses | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	831,000	1,714,000
Other cash restructuring expenses | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	48,000
Other cash restructuring expenses | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	267,000	1,070,000
Other cash restructuring expenses | Total cost of sales | Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring charges	564,000	596,000
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	1,207,000	1,980,000
Other cash restructuring expenses | Total selling, general and administrative expenses | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	902,000	1,675,000
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 | Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring charges	160,000	160,000
Other cash restructuring expenses | Total selling, general and administrative expenses | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	145,000	145,000
Asset impairments | Total cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring charges	553,000	2,811,000
Asset impairments | Total cost of sales | ESS
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	0
Asset impairments | Total cost of sales | Utility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	312,000	2,570,000
Asset impairments | Total cost of sales | Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring charges	241,000	241,000
Asset impairments | Total cost of sales | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0	$ 0