Commitments and Contingencies - Schedule of Restructuring Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 1,630	$ 492	$ 201
Restructuring expenses	2,306	1,577	1,438
Payments for restructuring	(1,168)	(1,286)
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	2,306	1,600	1,400
Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	1,424	0	0
Restructuring expenses	1,424	0
Payments for restructuring	0	0
Corporate, Non-Segment [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	1,424
UNITED STATES | Operating Segments [Member] | United States Electrical Construction And Facilities Services
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	30	452	0
Restructuring expenses	0	452
Payments for restructuring	(422)	0
UNITED STATES | Operating Segments [Member] | United States Mechanical Construction And Facilities Services
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	0	0	188
Restructuring expenses	0	180
Payments for restructuring	0	(368)
UNITED STATES | Operating Segments [Member] | United States Building Services
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	176	40	$ 13
Restructuring expenses	882	945
Payments for restructuring	(746)	$ (918)
UNITED STATES | Operating Segments [Member] | Employee Severance [Member] | United States Building Services
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 882