Acquisitions (2016 Acquisitions) - Additional Information (Detail) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) Acquisition	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Aggregate consideration for acquisitions | $		$ 42,211	$ 110,428
Contingent consideration | $		$ 15,400	$ 1,001
Acquisitions 2016 [Member]
Business Acquisition [Line Items]
Number of business acquisitions | Acquisition	3
Aggregate consideration for acquisitions | $	$ 42,200
Contingent consideration | $	15,400
Acquisitions 2016 [Member] | Maximum [Member]
Business Acquisition [Line Items]
Contingent consideration | $	$ 35,000
Acquisitions 2016 [Member] | Electric Power Infrastructure Services Business [Member]
Business Acquisition [Line Items]
Number of business acquisitions | Acquisition	2
Acquisitions 2016 [Member] | Electric Power Infrastructure Services Business [Member] | United States [Member]
Business Acquisition [Line Items]
Number of business acquisitions | Acquisition	1
Acquisitions 2016 [Member] | Electric Power Infrastructure Services Business [Member] | Canada [Member]
Business Acquisition [Line Items]
Number of business acquisitions | Acquisition	1
Acquisitions 2016 [Member] | Oil and Gas Infrastructure Services Business [Member] | United States [Member]
Business Acquisition [Line Items]
Number of business acquisitions | Acquisition	1