Subsequent Events - Additional Information (Detail)	3 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) Acquisition	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Subsequent Event [Line Items]
Consideration transferred or to be transferred cash and liabilities incurred except for contingent consideration		$ 42,211,000	$ 110,428,000
Contingent consideration		$ 15,400,000	$ 1,001,000
Scenario Forecast [Member]
Subsequent Event [Line Items]
Consideration transferred or to be transferred cash and liabilities incurred except for contingent consideration	$ 34,300,000
Scenario Forecast [Member] | Maximum [Member]
Subsequent Event [Line Items]
Contingent consideration	$ 4,500,000
Scenario Forecast [Member] | Electric Power Infrastructure Services Business [Member]
Subsequent Event [Line Items]
Number of business acquisitions | Acquisition	2
Scenario Forecast [Member] | Electric Power Infrastructure Services Business [Member] | Australia [Member]
Subsequent Event [Line Items]
Number of business acquisitions | Acquisition	1
Scenario Forecast [Member] | Electric Power Infrastructure Services Business [Member] | Canada [Member]
Subsequent Event [Line Items]
Number of business acquisitions | Acquisition	1