Business Combinations - Estimates of Acquired Intangible Assets (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 32,744	$ 10,667
Weighted Average Estimated Useful Life (yrs)	8 years	9 years
Trademarks and Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 17,190	$ 5,235
Weighted Average Estimated Useful Life (yrs)	15 years	15 years
Covenants Not-to-compete [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 1,847	$ 1,934
Weighted Average Estimated Useful Life (yrs)	5 years	5 years
Backlog [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 13,400
Weighted Average Estimated Useful Life (yrs)	1 year 6 months