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Schedule of Restructuring Activities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 1,138	$ 736	$ 1,138	$ 736	$ 1,558	$ 1,630
Restructuring expenses	536	119	605	567
Payments for restructuring			(1,025)	(1,461)
UNITED STATES \| Operating Segments [Member] \| United States Electrical Construction And Facilities Services [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	524	0	524	0	445	30
Restructuring expenses			268	0
Payments for restructuring			(189)	(30)
UNITED STATES \| Operating Segments [Member] \| United States Mechanical Construction And Facilities Services [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	268	0	268	0	0	0
Restructuring expenses			268	0
Payments for restructuring			0	0
UNITED STATES \| Operating Segments [Member] \| United States Building Services [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	0	35	0	35	412	176
Restructuring expenses			69	567
Payments for restructuring			(481)	(708)
UNITED STATES \| Operating Segments [Member] \| Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 346	$ 701	346	701	$ 701	$ 1,424
Restructuring expenses			0	0
Payments for restructuring			$ (355)	$ (723)